PSLE The figure shows taps A and B and an empty tank. At 8 p.m., tap A was turned on. Water flowed into the tank from tap A at a rate of 3.6 litres per minute. After 7 minutes, tap B was turned on. At 8.10 p.m., the tank was half filled with water.
- How many litres of water flowed out of tap B in 1 minute?
- At 8.30 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 8.10 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 3.6
= 25.2 ℓ
Duration that Tap B was turned
= 10 - 7
= 3 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 3 min
= 25.2 - 22.5
= 2.7 ℓ
Volume of water that flowed out in 1 min
= 2.7 ÷ 3
= 0.9 ℓ
Volume of water that flowed out of Tap B in 1 min
= 3.6 + 0.9
= 4.5 ℓ
(b)
Duration from 8.10 p.m. to 8.30 p.m. = 20 min
Volume of water that flowed out from 8.10 p.m. to 8.30 p.m.
= 20 x 0.9
= 18 ℓ
Volume of water left at 8.30 p.m.
= 22.5 - 18
= 4.5 ℓ
Fraction of the tank filled with water at 8.30 p.m.
=
4.545 =
110
Answer(s): (a) 4.5 ℓ; (b) 110