Madhya Pradesh Police Exam Model Paper 9

Given:
A and B can do a piece of work in 10 days and 15 days respectively
Concept Used:
One day work = 1/number of days taken by the worker to complete the whole work
Calculation:
One day work of A $=1/10$
One day work of B $=1/15$
One day work of $\mathit{A}+\mathit{B}=1/10+1/15$
$\Rightarrow \left(3+2\right)/30$
$\Rightarrow 1/6$
Now, 3 days work done by (A + B) is $3\times 1/6$
$\Rightarrow 1/2$
Hence, the part of work they can do together in 3 days is 1/2 of the whole work