PSLE The figure shows taps A and B and an empty tank. At 6 p.m., tap A was turned on. Water flowed into the tank from tap A at a rate of 4.2 litres per minute. After 6 minutes, tap B was turned on. At 6.10 p.m., the tank was half filled with water.
- How many litres of water flowed out of tap B in 1 minute?
- At 6.28 p.m., what fraction of the tank was filled with water?
(a)
Volume of the tank
= 60 x 35 x 20
= 42000 mℓ
= 42 ℓ
Volume of the tank at 6.10 p.m. when it was half filled with water
= 42 ÷ 2
= 21 ℓ
Volume of water by Tap A for 6 min
= 6 x 4.2
= 25.2 ℓ
Duration that Tap B was turned
= 10 - 6
= 4 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 4 min
= 25.2 - 21
= 4.2 ℓ
Volume of water that flowed out in 1 min
= 4.2 ÷ 4
= 1.05 ℓ
Volume of water that flowed out of Tap B in 1 min
= 4.2 + 1.05
= 5.25 ℓ
(b)
Duration from 6.10 p.m. to 6.28 p.m. = 18 min
Volume of water that flowed out from 6.10 p.m. to 6.28 p.m.
= 18 x 1.05
= 18.9 ℓ
Volume of water left at 6.28 p.m.
= 21 - 18.9
= 2.1 ℓ
Fraction of the tank filled with water at 6.28 p.m.
=
2.142 =
120
Answer(s): (a) 5.25 ℓ; (b) 120