10 men can complete a work in 7 days. But 10 women need 14 days to complete the same work. How many days will 5 men and 10 women need to complete the work?

A. 5
B. 6
C. 7
D. 8
Answer : C

Explanation :

Work done by 10 men in 1 day = 1/7
Work done by 1 man in 1 day = (1/7)/10 = 1/70
Work done by 10 women in 1 day = 1/14
Work done by 1 woman in 1 day = 1/140
Work done by 5 men and 10 women in 1 day = 5 * (1/70) + 10 * (1/140)
                                                                      = 5/70 + 10/140 = 1/7
=> 5 men and 10 women can complete the work in 7 days