$\frac{3}{4}$ part of the tank is filled by a motor pump in 15 minutes, then the rest part of the tank will be filled in

5 minutes

If \(\frac{3}{4}\) part is filled, then remaining part will be 1- \(\frac{3}{4}\) = \(\frac{1}{4}\)

Now, ATQ

\(\frac{3}{4}\) part is filled in ⇒ 15 min

1 par is filled in ⇒ 15 × \(\frac{4}{3}\) = 20 min

\(\frac{1}{4}\) part will be filled in ⇒ 20 × \(\frac{1}{4}\) = 5 min

OR, We can say,

Out of 4 parts, 3 part filled in 15 min, then remaining 1 part will be filled in \(\frac{15}{3}\) = 5 min.