Question

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

• A.
• B.
• C.
• D.

Answer 1

The correct option is C

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 = $(1-\frac{7}{15})=\frac{8}{15}$