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Estimation and Guessing

Estimation is making a rough calculation of the number, such as a value or quantity of something.

 
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Example 1:

We can estimate addition and subtraction by rounding.

        43 + 28 = _____

Rounding the numbers we get:

        40 + 30 = _____

        40 + 30 = 70

This is a close approximation of 43+28 which is equal to 71.

Example 2:

Sometimes we can quickly guess the correct answer to a math problem by simply starting the solution. Let's look at the following multiple choice math question.

What is the answer to the following multiplication problem

23 x 47 = _____  

(a) 1288     (b) 1081     (c) 8227

We don't need to actually do the whole multiplication. We can guess the answer as shown below:

           2 3
        x 4 7
     ---------
       XX 1

7 x 3 = 21

Last digit in the product must be 1.
So, (b) must be the correct answer.

 
 
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