PSLE The figure shows taps A and B and an empty tank. At 10 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 6 minutes, tap B was turned on. At 10.12 p.m., the tank was half filled with water.
- How many litres of water flowed out of tap B in 1 minute?
- At 10.30 p.m., what fraction of the tank was filled with water?
(a)
Volume of the tank
= 60 x 30 x 20
= 36000 mℓ
= 36 ℓ
Volume of the tank at 10.12 p.m. when it was half filled with water
= 36 ÷ 2
= 18 ℓ
Volume of water by Tap A for 6 min
= 6 x 3.9
= 23.4 ℓ
Duration that Tap B was turned
= 12 - 6
= 6 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 6 min
= 23.4 - 18
= 5.4 ℓ
Volume of water that flowed out in 1 min
= 5.4 ÷ 6
= 0.9 ℓ
Volume of water that flowed out of Tap B in 1 min
= 3.9 + 0.9
= 4.8 ℓ
(b)
Duration from 10.12 p.m. to 10.30 p.m. = 18 min
Volume of water that flowed out from 10.12 p.m. to 10.30 p.m.
= 18 x 0.9
= 16.2 ℓ
Volume of water left at 10.30 p.m.
= 18 - 16.2
= 1.8 ℓ
Fraction of the tank filled with water at 10.30 p.m.
=
1.836 =
120
Answer(s): (a) 4.8 ℓ; (b) 120