PSLE
The figure shows taps A and B and an empty tank. At 2 p.m., tap A was turned on. Water flowed into the tank from tap A at a rate of 3.9 litres per minute. After 7 minutes, tap B was turned on. At 2.15 p.m., the tank was half filled with water.

1. How many litres of water flowed out of tap B in 1 minute?
2. At 2.20 p.m., what fraction of the tank was filled with water?

(a)
Volume of the tank
= 60 x 30 x 25
= 45000 mℓ
= 45 ℓ

Volume of the tank at 2.15 p.m. when it was half filled with water
= 45 ÷ 2
= 22.5 ℓ

Volume of water by Tap A for 7 min
= 7 x 3.9
= 27.3 ℓ

Duration that Tap B was turned
= 15 - 7
= 8 min

Since there was a decrease in the volume of water in the tank, water flowed out of Tap B at a faster rate than that of Tap A.

Volume of water that flowed out in 8 min
= 27.3 - 22.5
= 4.8 ℓ

Volume of water that flowed out in 1 min
= 4.8 ÷ 8
= 0.6 ℓ

Volume of water that flowed out of Tap B in 1 min
= 3.9 + 0.6
= 4.5 ℓ

(b)
Duration from 2.15 p.m. to 2.20 p.m. = 5 min

Volume of water that flowed out from 2.15 p.m. to 2.20 p.m.
= 5 x 0.6
= 3 ℓ

Volume of water left at 2.20 p.m.
= 22.5 - 3
= 19.5 ℓ

Fraction of the tank filled with water at 2.20 p.m.
= ^19.5₄₅
= ¹³₃₀