Achievement Objectives
NA4-6: Know the relative size and place value structure of positive and negative integers and decimals to three places.
NA5-6: Know and apply standard form, significant figures, rounding, and decimal place value.
Description of Mathematics
Number Framework Stages7 and 8.
Required Resource Materials
Checking divsion by estimation (Material Master 8-4)
Activity
Using Number Properties
Problem: “The manager at the bookstore buys 69 books for $1,327. Estimate the price of one book.” Discuss why 69 is rounded to 70. (Answer: 70 has only 1 significant figure so tables will be able to be used in the next step.) Write 1 327 ÷ 70 on the board and discuss what 1 327 could be rounded to. (Possible answer: Rounding to say 1 300 or even 1 000 produces difficult divisions to do mentally. But rounding 1 327 to 1 400 produces the division 1 400 ÷ 7, which can be reduced to 14 ÷ 7 = 2 then adjusted to 1 400 ÷ 70 = 20.)
Examples: Worksheet (Material Master 8–4).
Understanding Number Properties:
Make up a four-digit decimal number divided by a two-digit decimal number problem of your own and explain how you would estimate the answer.
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