A is thrice as good as workman as B and therefore is able to finish a job in 60 days less than B. Working together, they can do it in? A is thrice as good as workman as B and therefore is able to finish a job in 60 days less than B. Working together, they can do it in:

A.  20 days 

B. 22 1/2 days

C.  25 days 

D.  30 days 

How do we approach towards these kinds?
Let $v$ be the working speed of $B$. Then, the working speed of $A$ is $3v$. The working speed of $A$ and $B$ together is $4v$.

Now, the time $A$ spends is $t$ (in days), and the time $B$ spends is $t+60$.

Since the speed and the time are inversely proportional, their product is constant, so $3v\cdot t=v(t+60)$.

Can you continue?
Let A be X where as b = 3x.
So,
3x – x = 60.
x = 30.
a = 30, b = 90.

Together they can do the work in 22 (1/2) days.

A is thrice as good as workman as B and therefore is able to finish a job in 60 days less than B. Working together, they can do it in