Explanation:

To solve this question, we can apply a short trick approach;
If M₁ persons can do a piece of work in D₁ days working and M₂ persons can do the same work in D₂ days then we have formula M₁D₁= M₂D₂
Given:
M₁ = 18, D₁= 24 days, M₂ = 27 boys, D₂ = ?
Now, as
M₁D₁= M₂D₂
18 × 24 = 27 × D₂
⇒ D₂ =  18 x 24 /27 = 16 days