Estimate to find the operator Revision | KS3 Maths Resources

## What you need to know

Things to remember:

• To estimate, we tend to round first, this is usually to the nearest 10, 100, 1000, etc. You should round in a way that makes the question easier to solve.
• Do the calculation for each operation $(\times,\div,+,-)$
• Use your estimate to determine which operator it should be.

Find an estimate to determine the missing operator

$137\_\_\_7=969$

“Operators” is the mathematical name for the symbols used for multiplication, division, addition, and subtraction.

We will do this question in four steps:

Step 1: Round your number appropriately

137 is close to 100, so this is how we’ll round.

7 is close to 10, so this is how we’ll round.

969 is close to 1000, so this is how we’ll round.

Step 2: Change the question by replacing the number with how we rounded them.

$100\_\_\_10=1000$

Step 3: Try the different operations

$100\times10=1000$

$100\div10=10$

$100+10=90$

$100-10=90$

Step 4: Determine the operation by choosing the operation with the closest answer.

Multiplication gave us the closest estimate to the actual answer.

Note: These were good estimate because the equation in Step 2 became true.

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## Example Questions

Step 1: Round your number appropriately

203 is close to 200, so this is how we’ll round.

178 is close to 200, so this is how we’ll round.

381 is closes to 400, s this is how we’ll round.

Step 2: Change the question by replacing the number with how we rounded them.

$200\_\_\_200=400$

Step 3: Try the different operations

$200\times200=40000$

$200\div200=1$

$200+200=400$

$200-200=0$

Step 4: Determine the operation by choosing the operation with the closest answer.

Addition gave us the best estimate for our answer and make Step 2 true.

Step 1: Round your number appropriately

234 is close to 200, so this is how we’ll round.

39 is close to 40, so this is how we’ll round.

6 is closes to 10, s this is how we’ll round.

Step 2: Change the question by replacing the number with how we rounded them.

$200\_\_\_40=10$

Step 3: Try the different operations

$200\times40=8000$

$200\div40=5$

$200+40=240$

$200-40=160$

Step 4: Determine the operation by choosing the operation with the closest answer.

Although none of the equation in Step 3 were the same as the equation in Step 2, division gave the closest answer is our best choice for the missing operator.

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