PSLE The figure shows taps A and B and an empty tank. At 9 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 9.14 p.m., the tank was half filled with water.
- How many litres of water flowed out of tap B in 1 minute?
- At 9.22 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 9.14 p.m. when it was half filled with water
= 42 ÷ 2
= 21 ℓ
Volume of water by Tap A for 8 min
= 8 x 4.2
= 33.6 ℓ
Duration that Tap B was turned
= 14 - 8
= 6 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 6 min
= 33.6 - 21
= 12.6 ℓ
Volume of water that flowed out in 1 min
= 12.6 ÷ 6
= 2.1 ℓ
Volume of water that flowed out of Tap B in 1 min
= 4.2 + 2.1
= 6.3 ℓ
(b)
Duration from 9.14 p.m. to 9.22 p.m. = 8 min
Volume of water that flowed out from 9.14 p.m. to 9.22 p.m.
= 8 x 2.1
= 16.8 ℓ
Volume of water left at 9.22 p.m.
= 21 - 16.8
= 4.2 ℓ
Fraction of the tank filled with water at 9.22 p.m.
=
4.242 =
110
Answer(s): (a) 6.3 ℓ; (b) 110