Mio can build a large shed in 7 days less then yuuko can. If they build it together it would take them 12 days. How long would it take each of them working alone?

Answer 1

m = y-7

1/m + 1/y = 1/12
1/(y-7) + 1/y = 1/12
y = 28
so, m = 21

check:
working together, in one day they can assemble 1/28 + 1/21 = 1/12 of the whole.