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Solves Problems and Reasons Logically
Lesson 24
Construct Solutions
  Objectives/Vocab/Tips > Examples 1 | 2 | 3 | 4 > Practice: 1 | 2 | 3 | 4 > Reflection

Example 3:

A man spent 1/3 of his money and then lost 2/3 of the remainder. He was left with $12.

  • How much did he start with?

Explain in detail how you found your answer using words, numbers, and/or pictures.

Once again, make sure that you fully understand the problem and what it is asking you to do. In this problem, someone is left with $12 after spending 1/3 of his money and losing 2/3 of the what was left. First of all, I think this guy should be a little more careful!

As you get ready to solve this one, look over the possible problem solving strategies and see which one(s) may help you the most.

One strategy is to work backwards. You are given the final amount of money the man had with events leading up to what he has left. Let's try working backwards starting with the money he has left and working backwards to the amount he started with.

As you begin to work backwards, you can even try to look at the facts you are given backwards starting with the money he had left. You know he had $12 at the end of the day. He lost 2/3 of the amount before he had $12. Therefore, you need to find a number that when multiplied by 2/3 equals $12. Algebraically, it can be set up as:

2/3 * Y = $12
(3/2)2/3 * Y = 12 * 3/2
Y = 36/2
Y = $18

If you are not able to use algebra to solve for the missing number, you may want to use guess and check to find the missing number that when multiplied by 2/3 equals 12.

We continue to work backwards and we know that the man had $18 before he lost his money and ended up with $12.

Now we need to basically do the same thing with the final step in finding his original amount of money. You know that after he spent money he ended up with $18. You know that $18 is 1/3 of the money he started with, so all you need to do is to multiply $18 by 3 or add $18 three times.

$18 x 3 = $54

By working backwards, you found out that the man started with $54.

In your answer, be sure to include the strategy you used to solve the problem, in this case working backwards. Be clear and specific as to the steps you took to arrive at the answer of $54. A problem like this may be a multiple choice problem with you having to explain how you solved it, a short answer problem, or even an extended response question. As long as you know how to solve the problem and explain your solution clearly you will receive all the assigned points.

Example 4 >>

 

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