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a) in which month was she born? b) how old is she?

This question has to be used by modular you use mod 12 to figure out what month she was born?

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Yes you do, since you know that there are twelve months in a year... – J. M. Dec 9 '11 at 0:20
You might want to consider going through your older questions and accepting those you've found helpful, by the way; that red "0%" is a bit distracting... – J. M. Dec 9 '11 at 0:22

Exactly. It is now December=11 (if January=0). You calculate $421 \pmod {12}$ and subtract to see what month she was born in.

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so is the answer november? – Briana791 Dec 9 '11 at 0:28
@Briana: Could you show us what you did to get to your answer? – J. M. Dec 9 '11 at 1:19
421 ( mod12) = 1 so wouldnt it be november because it is december now – Briana791 Dec 9 '11 at 1:35

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