PSLE The figure shows taps A and B and an empty tank. At 11 p.m., tap A was turned on. Water flowed into the tank from tap A at a rate of 4.5 litres per minute. After 5 minutes, tap B was turned on. At 11.10 p.m., the tank was half filled with water.
- How many litres of water flowed out of tap B in 1 minute?
- At 11.25 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 11.10 p.m. when it was half filled with water
= 42 ÷ 2
= 21 ℓ
Volume of water by Tap A for 5 min
= 5 x 4.5
= 22.5 ℓ
Duration that Tap B was turned
= 10 - 5
= 5 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 5 min
= 22.5 - 21
= 1.5 ℓ
Volume of water that flowed out in 1 min
= 1.5 ÷ 5
= 0.3 ℓ
Volume of water that flowed out of Tap B in 1 min
= 4.5 + 0.3
= 4.8 ℓ
(b)
Duration from 11.10 p.m. to 11.25 p.m. = 15 min
Volume of water that flowed out from 11.10 p.m. to 11.25 p.m.
= 15 x 0.3
= 4.5 ℓ
Volume of water left at 11.25 p.m.
= 21 - 4.5
= 16.5 ℓ
Fraction of the tank filled with water at 11.25 p.m.
=
16.542 =
1128
Answer(s): (a) 4.8 ℓ; (b) 1128