A work can be finished in 16 days by twenty women. The same work can be finished in fifteen days by sixteen men. The ratio between the capacity of a man and a woman is ___ ?

Work done by 20 women in 1 day = 1/16

Work done by 1 woman in 1 day = 1/(16×20)
Work done by 16 men in 1 day = 1/15

Work done by 1 man in 1 day = 1/(15×16)
Ratio of the capacity of a man and woman =1/(15×16) : 1/(16×20) = 1/15 : 1/20

= 1/3 :1/4 = 4:3