# When do you use the guess and check method?

Feb 10, 2015

You should use the guess and check method when you do not know how to solve a problem.

The guess and check method includes:

1. make a logical guess
3. adjust your guess based on results of #2 until you are correct

Example:

There are 20 children in the kindergarten class. The children are a mix of 5 year olds and 6 year olds. The total age of the children equals 108 years. How many 5 year olds are there?

Guess & check method:

1. Let's guess that there are 10 five year olds.
2. If there are 10 five year olds, there must be 10 six year olds since there are 20 children in total. Their combined age is equal to (10 x 5) + (10 x 6), or 110 years.
3. Since 110 years is greater than 108 (the correct answer), our initial guess was incorrect. To get closer to the correct answer, we need to guess a higher number of five year olds (since five years is less than six years).
4. Let's now guess that there are 12 five year olds.
5. If there are 12 five year olds, there must be eight six year olds since there are 20 children in total. Their combined age is equal to (12 x 5) + (8 x 6), or 108 years. Therefore, the correct answer is 12 five year olds.