Question

If $A$ and $B$ together can complete a piece of work in $15$ days and $B$ alone in $20$ days, then in how many days can $A$ alone complete the work?

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

Answer 1

The correct option is A $60$

$(A+B)$ complete a work in $15$ days.
$\Rightarrow$ One day's work of $(A+B)=\frac{1}{15}$
$B$ completes the work in $20$ days.
$\Rightarrow$ One day's work of $B=\frac{1}{20}$
Now, one day's work of $A$
$=\frac{1}{15}-\frac{1}{20}=\frac{1}{60}$
Thus, $A$ can complete the work in $60$ days.