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 3.9 litres per minute. After 8 minutes, tap B was turned on. At 3.12 p.m., the tank was half filled with water.
- How many litres of water flowed out of tap B in 1 minute?
- At 3.24 p.m., what fraction of the tank was filled with water?
(a)
Volume of the tank
= 60 x 40 x 25
= 60000 mℓ
= 60 ℓ
Volume of the tank at 3.12 p.m. when it was half filled with water
= 60 ÷ 2
= 30 ℓ
Volume of water by Tap A for 8 min
= 8 x 3.9
= 31.2 ℓ
Duration that Tap B was turned
= 12 - 8
= 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
= 31.2 - 30
= 1.2 ℓ
Volume of water that flowed out in 1 min
= 1.2 ÷ 4
= 0.3 ℓ
Volume of water that flowed out of Tap B in 1 min
= 3.9 + 0.3
= 4.2 ℓ
(b)
Duration from 3.12 p.m. to 3.24 p.m. = 12 min
Volume of water that flowed out from 3.12 p.m. to 3.24 p.m.
= 12 x 0.3
= 3.6 ℓ
Volume of water left at 3.24 p.m.
= 30 - 3.6
= 26.4 ℓ
Fraction of the tank filled with water at 3.24 p.m.
=
26.460 =
1125
Answer(s): (a) 4.2 ℓ; (b) 1125