Bunuel wrote:
Mark and Kate individually take 12 hours more and 27 hours more, respectively, to complete a certain project than what they would have taken to complete the same project working together. How many hours do Mark and Kate take to complete the project, working together?
(A) 12
(B) 16
(C) 18
(D) 24
(E) 39
Say time they take when working together = T
Mark takes 12 extra hours working alone because in 12 hrs, he does what Kate does in T hrs. So if ratio of their time taken = 12:T,
RateM/RateK = T/12
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