PSLE The figure shows taps A and B and an empty tank. At 3 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 8 minutes, tap B was turned on. At 3.15 p.m., the tank was half filled with water.
- How many litres of water flowed out of tap B in 1 minute?
- At 3.26 p.m., what fraction of the tank was filled with water?
(a)
Volume of the tank
= 60 x 35 x 25
= 52500 mℓ
= 52.5 ℓ
Volume of the tank at 3.15 p.m. when it was half filled with water
= 52.5 ÷ 2
= 26.25 ℓ
Volume of water by Tap A for 8 min
= 8 x 4.2
= 33.6 ℓ
Duration that Tap B was turned
= 15 - 8
= 7 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 7 min
= 33.6 - 26.25
= 7.35 ℓ
Volume of water that flowed out in 1 min
= 7.35 ÷ 7
= 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 3.15 p.m. to 3.26 p.m. = 11 min
Volume of water that flowed out from 3.15 p.m. to 3.26 p.m.
= 11 x 1.05
= 11.55 ℓ
Volume of water left at 3.26 p.m.
= 26.25 - 11.55
= 14.7 ℓ
Fraction of the tank filled with water at 3.26 p.m.
=
14.752.5 =
725
Answer(s): (a) 5.25 ℓ; (b) 725