Posted by **Lexi** on Tuesday, September 30, 2008 at 12:35am.

When a certain number N is divided by d, the remainder is 7. If the original number N is multiplied by 5 and then divided by d, the remainder is 10.

Find d.

- Maths -
**David Q**, Tuesday, September 30, 2008 at 2:00pm
The answer is d=25; N is any of 7, 32, 57, 82, 107, 132 etc etc. It was set up in a spreadsheet and arrived at by trial and error, so just knowing the answer probably won't get many marks. I'd be interested to know if anyone else can produce a formula for deriving the solution algebraically - because I can't see how to do it either.

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