Make an Organised list

Numeracy - Problem Solving - Thursday 2nd February 2017

Guess and Check Strategy

"Guess and Check" is a problem-solving strategy that you can use to solve mathematical problems by guessing the answer and then checking that the guess fits the conditions of the problem. For example, the following problem would be best solved using guess and check:

Of 25 rounds at the regional spelling contest, the Mighty Brains tied 3 rounds and won 2 more than they lost. How many rounds did the Mighty Brains win?

Problem 1:

Ben knows 100 baseball players by name. Ten are Red Sox. The rest are Blue Jays and Diamondbacks. He knows the names of twice as many Diamondbacks as Blue Jays. How many Blue Jays does he know by name?

When you use the strategy of guess and check, you should keep a record of what you have done. It might be helpful to use a chart or table.

Steps to take to solve this problem:

1. Understand the problem

Find key pieces of information needed to solve the problem - this could mean that you need to read the original problem several times or put it into your own words.

For example, "I know there are twice as many Diamondbacks as Blue Jays. There are 10 Red Sox. The number of Blue Jays and Diamondbacks should equal 90."

2. Choose a strategy

3. Solve the problem

Now, solve the problem. You may want to set up a table to record the guesses.

Guess Number	Blue Jays	Diamondbacks	Red Sox	Total
First Guess	10	20	10	40

Guess a greater number of Blue Jays.

Guess Number	Blue Jays	Diamondbacks	Red Sox	Total
First Guess	10	20	10	40
Second Guess	20	40	10	70

Now guess a greater number of Blue Jays.

Guess Number	Blue Jays	Diamondbacks	Red Sox	Total
First Guess	10	20	10	40
Second Guess	20	40	10	70
Third Guess	40	80	10	130

Now guess a number lesser than 40 and greater than 20.

Guess Number	Blue Jays	Diamondbacks	Red Sox	Total
First Guess	10	20	10	40
Second Guess	20	40	10	70
Third Guess	40	80	10	130
Fourth Guess	30	60	10	100

That is the answer.

4. Check

Read the problem again to be sure the question was answered.

Yes, I found the number of Blue Jays.

Check the math to be sure it is correct.

30 doubled is 60. 30 + 60 + 10 = 100

Determine if the best strategy was chosen for this problem, or if there was another way to solve the problem.

Guess and check was a good way to solve this problem.

5. Explain

The last step is explaining how you found the answer. Write a paragraph describing the steps and how decisions were made throughout the process. Justify your answers.

YOUR TURN:

Try to solve this problem using the strategy of Guess and Check:

Of 25 rounds at the regional spelling contest, the Mighty Brains tied 3 rounds and won 2 more than they lost. How many rounds did the Mighty Brains win?

Independent Task:

WALT - Guess and check

GOT it Resource - Problem Sheets 1