3-2 Estimating Costs Day 1

3-2 Estimating Costs Day 1

Multiple Choice

Is 18 closer to 10 or 20?

• 10

• 20

• same distance

Multiple Choice

Is 21 closer to 20 or 30?

• 20

• 30

• same distance

Multiple Choice

Is 188 closer to 180 or 190?

• 180

• 190

• Same distance

Multiple Choice

Is 105 closer to 100 or 110?

• 100

• 110

• same distance

Multiple Choice

Is 2,777 closer to 2,770 or 2,780?

• 2,770

• 2,780

• same distance

Multiple Choice

Is 2,850 closer to 2,800 or 2,900?

• 2,800

• 2,900

• same distance

Math Message

Complete Math Journal Page 67.

When might you use an estimate?

• When I need to solve problems in my head

• When I do not need an exact answer

• to check whether an answer to an addition or subtraction problem makes sense.

Reasonable Estimates

• The close-but-easier numbers you choose depend on how you add in your head and how close you want the estimate to be.

• The strategy you choose may depend on the situation in the problem.

Poll

Which of the estimates was easier to do in your head?

• 320+490

• 300+500

Poll

Which of the estimates are close enough to decide whether the answer was reasonable?

• 300+500

• 490+320

Math Master page 80

How could you help Ann?

Do you need an exact answer to decide wheter the answer makes sense?

How could you use your estimate to decide whether Ann's answer is reasonable?