Given: A swimming pool can be filled by tap P and tap Q together in 36 minutes P open for 40 minutes and Q open for 30 minutes Concept: If a tap can fill a tank in x hours, then the tank filled by the tap in 1 hour =
1
x
of the total tank. Calculation: Let the tap Q fill the tank in ‘a’ minutes. Part of the swimming pool filled by tap P in 1 minute =
1
36
−
1
a
According to the question, ⇒30×
1
a
+40(
1
36
−
1
a
)=1 ⇒
30
a
+
10
9
−
40
a
=1 ⇒
40
a
−
30
a
=
10
9
−1 ⇒
10
a
=
1
9
⇒a=90minutes ∴ Tap Q can fill the tank in 90 minutes.