in a school each class has 7 charts to display on a notice board. Each chart must have 9 thumb tacks to support it.

a) How many tacks are needed if three classes have to display their charts on the notice board?

b) The three classes have a total of 171 tacks. How many charts could not be placed on the board?

3 answers

a) 3 * 7 * 9 = 189

b) 189 - 171 = 18

18/9 = ?
18 over 9
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