Using Materials

Problem: “Ana goes Christmas shopping. She spends $345.60 on toys for her children and comes home with $208.95. How much money did she have to start with?”

Write ? – 345.60 = 208.95 on the board. Have the students cut a strip of paper, representing Ana’s unknown starting amount.

Cut off a piece and write $345.60 on it.

Discuss what goes on the other piece. (Answer: $208.95.)

Discuss what the starting amount must have been. (Answer: $345.60 + $208.95 = $554.55.)

Examples: Word stories and recording for: ? – 345 = 789

? – 456 = 102

? – 67.9 = 43.19

? – 67 = 90

? – 1 000 = 3 000

? – 200 = 560 ...

Using Imaging

Examples: Imagine the strips to solve these problems: Word stories and recording for:

? – 200 = 600

? – 220 = 230

? – $7.90 = $3.10

? – 111 = 238

 ? – 10 000 = 4 500 ...

Using Number Properties

Examples: Don’t use calculators for the fraction problems. Word stories and recording for:

? – 212.98 = 600.0034

? – 200.08 = 45.89

? – 7.9909 = 3.1091

 ? – 10 = 3/4

? – 2 1/3 = 1/3

? – 0.04 = 0.0009 ...

Understanding Number Properties:

a and b stand for any numbers: â–¡ – a = b. How would you work out

the number to put in the box? (Answer: I would work out the answer to a + b.)