PSLE The figure shows taps A and B and an empty tank. At 7 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 7 minutes, tap B was turned on. At 7.10 p.m., the tank was half filled with water.
- How many litres of water flowed out of tap B in 1 minute?
- At 7.28 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 7.10 p.m. when it was half filled with water
= 36 ÷ 2
= 18 ℓ
Volume of water by Tap A for 7 min
= 7 x 2.7
= 18.9 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
= 18.9 - 18
= 0.9 ℓ
Volume of water that flowed out in 1 min
= 0.9 ÷ 3
= 0.3 ℓ
Volume of water that flowed out of Tap B in 1 min
= 2.7 + 0.3
= 3 ℓ
(b)
Duration from 7.10 p.m. to 7.28 p.m. = 18 min
Volume of water that flowed out from 7.10 p.m. to 7.28 p.m.
= 18 x 0.3
= 5.4 ℓ
Volume of water left at 7.28 p.m.
= 18 - 5.4
= 12.6 ℓ
Fraction of the tank filled with water at 7.28 p.m.
=
12.636 =
720
Answer(s): (a) 3 ℓ; (b) 720