PSLE The figure shows taps A and B and an empty tank. At 2 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 2.15 p.m., the tank was half filled with water.
- How many litres of water flowed out of tap B in 1 minute?
- At 2.29 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 2.15 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
= 15 - 5
= 10 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 10 min
= 22.5 - 21
= 1.5 ℓ
Volume of water that flowed out in 1 min
= 1.5 ÷ 10
= 0.15 ℓ
Volume of water that flowed out of Tap B in 1 min
= 4.5 + 0.15
= 4.65 ℓ
(b)
Duration from 2.15 p.m. to 2.29 p.m. = 14 min
Volume of water that flowed out from 2.15 p.m. to 2.29 p.m.
= 14 x 0.15
= 2.1 ℓ
Volume of water left at 2.29 p.m.
= 21 - 2.1
= 18.9 ℓ
Fraction of the tank filled with water at 2.29 p.m.
=
18.942 =
920
Answer(s): (a) 4.65 ℓ; (b) 920