Coupon Combinations

This activity helps students to develop strategies they can use when solving addition problems. Many older students need to revisit the strategies used for addition and subtraction rather than simply applying a memorised routine that gets them the correct answer. Mathematicians are able to see relationships and connections between the problem they are solving and ideas they have met before. So, you need to encourage
students learning mathematics to think mathematically.
Encourage the students to work mentally with the problems rather than solve them using a vertical algorithm because they will not use a thinking strategy if they use the vertical algorithm. If students are not able to keep all the numbers in their heads, model a recording method that reflects the thinking strategy used. For example, Simon’s thinking could be recorded as:

Answers to Activity

1. 285 + 400 = 685
396 is 4 less than 400
685 – 4 = 681 tokens
2. a. 523 + 400 = 923
923 + 40 = 963
963 + 8 = 971 tokens
b. Two ways are:
i. 448 is 2 less than 450
523 + 450 = 973
973 – 2 = 971 (rounding and compensating)
ii. 500 + 400 = 900
23 + 48 is close to 25 + 50 = 75
75 – 2 – 2 = 71
900 + 71 = 971 (place value and rounding)
3. Lawrence and Charlotte can combine their tokens:
285 + 523 = 808. Emeli and Simon can combine their tokens: 448 + 396 = 844.