Sunday, February 9, 2014

System of Linear Equations Word Problems

Here are some difficult systems of equations word problems for those who want a challenge! These problems involve the usage of logic, reasoning, and problem solving skills. These questions are based on using fairly simple concepts, such as rate x time = distance. Answers to these problems will be posted next week. Hope you enjoy!

System of Linear Equation Word Problems:


1. At a dance party, a group of boys and girls exchange dances as follows: one boy dances with 5 girls, a second boy second with 6 girls, and so on, the last boy dancing with all the girls. If b represents the number of boys and g the number of girls, then find b in terms of g.


2. George Washington was born 11 years before Thomas Jefferson. In 1770, Washington's age was 3 more than 7 times the age of Jefferson in 1748. What was the sum of the two men's ages in 1750.

3. Four pounds of onions costs the same as 2 pounds of string beans. At the same time, 1 pound of string beans costs 3 times as much as a pound of potatoes, while 1 pound of onions costs 4 cents less than 2 pounds of potatoes. What is the total cost of 1 pound of each of the vegetables?

4. Find two consecutive odd integers such that 1/3 the smaller plus twice the larger equals 7 more than the sum of the two numbers.

5. In a basketball game, the U.S. has 4 times as many points as Croatia. A Croatian makes a basket for 3 points, at which point the United States only has 3 times as many points. How many points does the U.S. have?

6. Mike and Joey bought identical loaves of bread and packages of bologna. Mike made sandwiches with 5 slices of bologna and had 4 slices of bread left when he ran out of meat. Joey made sandwiches with 4 slices of bologna and had 4 slices of meat when he ran out of bread. Each boy only started with one loaf and each sandwich has two slices of bread. How many slices of bread were in each loaf?

7. Sue has $3.08 in pennies, nickels, and quarters. She has 4 more pennies than quarters and one more nickel than pennies. How many nickels does she have?

8. K takes 30 minutes less time than M to travel a distance of 30 miles. K travels 1/3 mile per hour faster than M. If x is K's rate of speed in miles per hour, then find K's time for the distance in terms of x. 

9. What is the value of x if 1 minus the reciprocal of (1–x) equals the reciprocal of (1–x)?

10. A train traveling from Aytown to Beetown meets with an accident after 2 hour. The train is stopped for 30 minutes, after which it proceeds at four-fifths of its usual rate, arriving at Beetown 2 hours late. If the train had covered 80 miles more before the accident, it would have been just one our late. What is the usual rate of the train?

11. Adam can do a job in 10 days, while Brenda takes 15 days to do it. After Brenda works 3 days, Adam and Brenda work together to finish the job. How many days did Adam work?

12.A car travels 120 miles from A to B at 30 miles per hour but returns the same distance at 40 miles per hour . What is the average speed for the round trip?

13. One car left a city at 2:00 pm and traveled at an average speed of 40 miles per hour. A second car left at 4:00 pm, traveled the same route, and overtook the first car at 9:00 pm. What was the average speed in miles per hour of the second car?

14. A man can do a job in 9 days and his son can do the same job in 16 days. They start working together. After 4 days, the son leaves and the father finishes the job alone. How many days does the man take to finish the job?

15. Twenty-five women did 1/5 of a job in 8 days. Then, because of an emergency, it became necessary to complete the job in the next 20 days. How many additional women needed to be added to the crew of 25 to accomplish this?

16. Two bicyclists are seven-eighths of the way through a mile-long tunnel when a train approaches the closer end at the 40 mph. The riders take off at the same speed in opposite directions, and each escapes the tunnel as the train passes them. How fast did they ride?

17. A train, x meters long, traveling at a constant speed, takes 20 seconds from the time it first enters a tunnel 300 meters long until the time it completely emerges from the tunnel. One of the stationary ceiling lights in the tunnel is directly above the train for ten seconds. Find x. 

18. Two men starting at a point on a circular 1-mile race track walk in opposite with uniform speeds and meet in 6 minutes, but if they walk in the same direction, it requires one hour for the faster walker to gain a lap. What is the rate of the slower walker?

19. A crew of 30 people can build a certain road in 60 days. After the tenth day the plans are changed; the company wants the road built in 30, not 60, days. How many more people must be hired?

20. Jack and Jill went up the hill at a rate of 8 units per minute. They came tumbling down at a rate of 8 units per second. What was their average rate, in units per minute, for the round trip?

21. Two dogs, each traveling 10 ft/sec, run toward each other from 500 feet apart. As they run, a flea flies from the nose of one dog to the nose of the other at 25 ft/sec. The flea flies between the dogs in this manner until it is crushed when the dogs collide. How far did the flea fly?

22. Find the ordered pair (x, y) that is the solution of the system:


x + 2y = 11
   xy      12

2x – 2y = 2
    xy      3

23. Find the value of x/y if (3/√y) — (1/x) = 2/(xy)

24. When three numbers are added tow at a time, the sums are 29, 46, and 53. What is the sum of all three numbers?

25. Each valve A, B, and C, when open, releases water into a tank at its own constant rate. With all three valves open, the tank fills in 1 hour. With only valves A and C open, it takes 1.5 hours. With only valves B and C open, it takes 2 hours. How long will it take to fill the tank with only valves A and B open?

Sunday, February 2, 2014

Japanese Multiplication Trick

Hey guys,
Sorry it's been almost 2 years since my last post. These last several months, I've been very busy with my classes and outside activities. But today, I hope my visual method of multiplying numbers makes up for this delay.

This is a method used by the Japanese on how to multiply two numbers visually using diagonal lines! It's very interesting, and I thought it would be worthwhile to share it with you today.

Problem: 12 x 13

Step 1: "Draw" the first number
Draw diagonal lines from left to right angling downwards representing the number 12. One diagonal line (tens place) should be by itself, and the other two (ones place) should be grouped together just a little bit farther up and away, as shown below.


Step 2: "Draw" the second number.
Draw diagonal lines from left to right angling upwards representing the number 13. One diagonal line (tens place) should be by itself, and the other three (ones place) should be grouped together just a bit farther down and away, as shown below. Keep in mind that these lines must intersect with the previously drawn ones.
Step 3: Group the intersections
Group the black and green line intersections depending on however they line up with each other. Refer to the diagram below.
Step 4: Count the intersections.
Count the number of intersections in each group from right to left. The number of intersections on the farthest right would be the ones place, the number to the left of that would be the tens place, and so on. The number of intersections are actually the digits that make up the product of the original problem. Once you have the digits, you have your answer.
Therefore, the answer to 12 x 13 = 156. 
This method can be used to find the product of any ANY TWO NUMBERS. The only difference is that the intersections may be grouped up differently, and the number of intersections in each group may exceed 9. If this occurs, simply carry it over to the next left place value in the final answer. 

Hope this helps! I do look forward to being active on my blog once again. Feel free to leave your comments below or follow my blog. Thanks! 

Saturday, June 2, 2012

Brain Teasers: Equation Gone Wrong

Hey all! Can anyone figure out what went wrong?

a = b
ab = b^2
ab - a^2 = b^2 - a^2
a(b - a) = (b - a)(b + a)
a = b + a
                                                          a = b;          a = a + a
a = 2a
1 = 2?

What happened?






Solution: Look at Steps 4 and 5 in my justification above:

a(b - a) = (b - a)(b + a)
a = b + a

If a = b, then b - a = 0, so the real justification would be:

a(0) = (0)(b + a)
0 = 0

This means I divided by 0 in my justification, which is impossible according to the laws of mathematics.

Hope you enjoyed!

Fast Facts

Hey! Here are some fun math tips.


Fact 1:

1 = 1
1 + 3 = 4
1 + 3 + 5 = 9
1 + 3 + 5 + 7 = 16
1 + 3 + 5 + 7 + 9 = 25

See? The sum of odd consecutive numbers starting from 0, will always be a perfect square number no matter how far you go. Check it out!

Fact 2:


4% of 100 = 100 % of 4
6% of 38 = 38% of 6
5% of 10 = 10% of 5
7% of 50 = 50% of 7

Catch the drift?

Fact 3:

(a * b) * (c * d) = 100(ac) + 10(ad + bc) + (bd)

This is just the Rainbow Method simplified into an equation!

Fact 4: 



To square 2 digit numbers ending with ‘5’ (Example: 75 × 75)
1.  Take the first digit ‘7’ multiply by the number after ‘7’ => 7 × 8 = 56 
Now add 25 after the number. 56(25) = 5625
Hope you all enjoyed!

Wednesday, April 11, 2012

Factoring Quadratic Expressions: Box Method

Hello all. Sorry for not posting a blog in a while. I've been having a lot on my hands and I couldn't find the time to get to this. Now I do :). Today, I will be teaching you all a technique on how to factor quadratic expressions in the form ax^2 + bx + c.

The example we will be using is: 2x^2 - 5x + 3.

To factor this expression, we will use the Box Method. First, create a box with 5 squares.

Step 1: Insert the first term in the 2nd square and the last term in the 5th square. Then multiply those terms together, and put the product to the side of the box as shown:
Step 2: Now find two terms that multiply together to get the product on the right, BUT ALSO, add up together to get the middle term in the original expression. In this case, we need to find two terms that if multiplied, get us 6x^2, but also if added together, get us -5x. Put each term on boxes 3 and 4. It doesn't matter which term goes in which box.

Step 5: Now its time to calculate the factorization of this equation. First, calculate the GCF of the two terms of the top 2 boxes and put the GCF to the left of Box 2. Then do the same thing with the bottom 2 boxes and put the GCF to the left of Box 4. (I made a typo: the GCF next to Box 4 is -3, and not 3).
Step 6: Now you have to calculate the GCF of the two terms of the left 2 boxes and put the GCF under Box 4. Then do the same thing with the right 2 boxes and put the GCF under Box 5. 
Step 7: Now we know the numbers of our factoring. Just put parentheses around the GCFs to the left of the square to get the first "term" in the factoring, and put parentheses around the GCFs under the square to the get the second "term" in the factoring.

Therefore, if we factor 2x^2 - 5x + 3, we get: (2x - 3)(x - 1)

Thanks for reading this method on factoring! If you have any questions, please post comments down below.

Tuesday, November 1, 2011

Multiplication: Base Method 1

Hello. Today I am going to teach a new two way trick on how to do the Base Method. The Base Method is a way to use bases to multiply numbers. Some people prefer the Rainbow Method over the Base Method, but that is up to you.

Example: 98 x 95

Step 1:  First, find the closest base of the two factors that is higher than the two factors. A base is a number that is either 10 or a power of 10. This includes 100, 1000, 10000, etc because they are all powers of 10. In this case, the closest base of the two factors that is higher than the two factors is 100.

Step 2: Pick one of the factors in the problem. Figure out that factor minus the base you chose in the previous step. Place that number on top of the factor you chose in the beginning of the step.
                                                                                             -5
                                                                     Example: 98 x 95
As you can see, 95 (the factor I chose) - 100 (the base) =-5. Therefore I put that number on top of 97.

Step 3: Repeat Step 2 for the other factor in the problem.
                                                                                     -2       -5
                                                                     Example: 98 x 95
Step 4: Now do something I like to call "cross-adding". It's when you pick any number and add it to whatever is diagonal from it. For example, if you choose 95, you would add -2, because -2 is diagonal of 95, as shown below:
                                                                                    -2     -5
                                                                     Example: 98 x 95

95 is diagonal of -2. 95 +-2 = 93.

That sum of those 2 numbers is the first 2 digits of your answer.
                                                                 
                                                                  -2     -5
                                                  Example: 98 x 95                Answer: 93

Step 5: Pay attention to your base. Count the number of zeros your base has. This tells you how many digits your answer has left.

                                                      Base: 100.                     Answer: 93_ _

Step 6: To figure out the last 2 digits of your answer. Simply multiply the 2 numbers at the top.
                                                                                     -2     -5
                                                                    Example: 98 x 95   
                                                                        -5 x -2 = 10

                                                                     Answer:       9310

The answer is 9310. Hope this helped! If you have any questions, please post a comment below about it. Thanks!
             

Monday, October 31, 2011

Multiplication: Rainbow Method

 Hello! Today I will teach you how to multiply quicker than you already can with a method known as the Rainbow Method. This is a shortcut on how to multiply any 2 digit number with any other two digit number.

Example: 23 x 55

Step 1: To calculate the first two digits of your answer, multiply the first digit of the first factor to the first digit of the second factor. Then leave a space after the answer.

23 x 55     Answer: 10_

Step 2: To calculate the last digit of your answer, multiply the last digit of the first factor to the last digit of the second factor. If its a two digit number, carry over the tens place digit to the space before.
                                                                                       1
23 x 55        Answer: 10_5


Step 3: Now, to calculate the final digit of the answer (the space) you will use the Rainbow Method. Simply multiply the first digit of the first factor to the last digit of the last factor, and add that to the product of the last digit of the first factor to the first digit of the last factor, as shown below:

                                              

This shows that you are adding "2 x 5"(as shown in the outer rainbow line on the picture) to "3 x 5"(as shown in the inner rainbow line on the picture). The sum is 25. This is what you put in the space in the answer. Since it is a 2 digit number, carry over the tens place digit of this number to the place before in the answer.

                                                                                      21
23 x 55          Answer: 1055 

Step 4: Now do your finishing touches on your answer by adding the digits you carried over to the digits below them, as shown below.

                                                                                                                   21
23 x 55          Answer: 1055 
                                                                        
                                                                          True Answer: 1265

The answer is therefore 1265. I hope you've learned how to use this method! If you have any questions, please post a comment below about it. Thanks!