PSLE
The figure shows taps A and B and an empty tank. At 3 p.m., tap A was turned on. Water flowed into the tank from tap A at a rate of 2.7 litres per minute. After 6 minutes, tap B was turned on. At 3.15 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 3.21 p.m., what fraction of the tank was filled with water?

(a)
Volume of the tank
= 60 x 30 x 15
= 27000 mℓ
= 27 ℓ

Volume of the tank at 3.15 p.m. when it was half filled with water
= 27 ÷ 2
= 13.5 ℓ

Volume of water by Tap A for 6 min
= 6 x 2.7
= 16.2 ℓ

Duration that Tap B was turned
= 15 - 6
= 9 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 9 min
= 16.2 - 13.5
= 2.7 ℓ

Volume of water that flowed out in 1 min
= 2.7 ÷ 9
= 0.3 ℓ

Volume of water that flowed out of Tap B in 1 min
= 2.7 + 0.3
= 3 ℓ

(b)
Duration from 3.15 p.m. to 3.21 p.m. = 6 min

Volume of water that flowed out from 3.15 p.m. to 3.21 p.m.
= 6 x 0.3
= 1.8 ℓ

Volume of water left at 3.21 p.m.
= 13.5 - 1.8
= 11.7 ℓ

Fraction of the tank filled with water at 3.21 p.m.
= ^11.7₂₇
= ¹³₃₀