math
posted by clive .
A and B can do a piece of work in 12 days. They started to work together but A left after a few days. If B alone worked for 20 days, the whole work was finished in 24 days. How long would A take to complete the work???
question is really confusing :/

math 
Steve
1/a + 1/b = 1/12
So, if A left after n days, A&B did n/12 of the work.
20/b = 1  n/12
240 = 12b  nb
b = 240/(12n)
so,
1/a + (12n)/240 = 1/12
240 + (12n)a = 20a
a = 240/(8+n)
I agree the question is confusing. The exact conditions seem ambiguous.
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