Question

$A$ can complete a certain job in $12$ days. $B$ is $60$ % more efficient than $A.B$ can complete the work alone in:

• A. $6$ days
• B. $6.25$ days
• C. $7.2$ days
• D. $7.5$ days

Answer 1

The correct option is D $7.5$ days

Ratio of times taken by A and B $=$$160:100$ $=$$8:5$.
Suppose B alone takes $x$ days to do the job.
Then, $8:5$ $::12:x$ $\to$$8x=5\times 12$ $\to$ $x=7.5days$