Math CentralQuandaries & Queries


Question from Kevin, a parent:

Duwayne wrote a two-digit number. He multiplied it by 3, added 18, and divided by 8. His final answer was 9. What number did Duwayne write?


I can help get you started.

Here is Duwayne's work.

First number

line 1 ______

multiply by 3

result: line 2 ______

add 18

result: line 3 ______

divide by 8

answer: 9

The subject line of your email was "work backward" and that's the way I would solve this. In the last step he took the number in line 3, divided it by 8 and got the answer 9. What number was in line 3? Once you know this ask yourself, what number was in line 2?


I hope this helps,

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