Question

A can do a work in 15 days and B in 20 days. If they work on it together for 4 days then the fraction of the work that is left is:

• A.
• B.
• C.
• D.
• E.

Answer 1

The correct option is D

A’s 1 day’s work = $\frac{1}{15}$
B’s 1 day’s work = $\frac{1}{20}$
(A+B)’s 1 day’s work = $(\frac{1}{15}+\frac{1}{20})=\frac{7}{60}$
(A+B)’s 4 days’ work = $(\frac{7}{60}\times 4)=\frac{7}{15}$
∴ Remaining work = $(1-\frac{7}{15})=\frac{8}{15}$