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. $\frac{1}{4}$
• B. $\frac{1}{10}$
• C. $\frac{7}{15}$
• D. $\frac{8}{15}$

Answer 1

The correct option is D

$\frac{8}{15}$

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 day's work $=(\frac{7}{60}\times 4)=\frac{7}{15}.$
Therefore, Remaining work $(1-\frac{7}{15})=\frac{8}{15}.$