P is 30% more efficient than Q. P can complete a work in 23 days. If P and Q work together, how much time will it take to complete the same work?

A. 9
B. 11
C. 13
D. 15
Answer : C

Explanation :

Work done by P in 1 day = 1/23
Let work done by Q in 1 day = q
q * (130/100) = 1/23
=> q = 100/(23*130) = 10/(23*13)
Work done by P and Q in 1 day = 1/23 + 10/(23*13) = 23/(23*13)= 1/13
=> P and Q together can do the work in 13 days