Question

$A$ and $B$ can together do a piece of work in $15$ days. $B$ alone can do it in $20$ days. Then $A$ alone can do it in

• A. $30$ days
• B. $40$ days
• C. $45$ days
• D. $60$ days

Answer 1

Answer: (D)

$60$ days

${(A+B)}^{\prime }s$ one day work $=\frac{1}{15}$
$B^{\prime }s$ one day work $=\frac{1}{20}$
$\therefore A^{\prime }s$ one day work $=(\frac{1}{15}-\frac{1}{20})=\frac{1}{60}$
So, $A$ alone can do the work in $60$ days.
Hence, option 'D' is correct.