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 3.6 litres per minute. After 6 minutes, tap B was turned on. At 9.15 p.m., the tank was half filled with water.
- How many litres of water flowed out of tap B in 1 minute?
- At 9.23 p.m., what fraction of the tank was filled with water?
(a)
Volume of the tank
= 60 x 30 x 15
= 27000 mℓ
= 27 ℓ
Volume of the tank at 9.15 p.m. when it was half filled with water
= 27 ÷ 2
= 13.5 ℓ
Volume of water by Tap A for 6 min
= 6 x 3.6
= 21.6 ℓ
Duration that Tap B was turned
= 15 - 6
= 9 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 9 min
= 21.6 - 13.5
= 8.1 ℓ
Volume of water that flowed out in 1 min
= 8.1 ÷ 9
= 0.9 ℓ
Volume of water that flowed out of Tap B in 1 min
= 3.6 + 0.9
= 4.5 ℓ
(b)
Duration from 9.15 p.m. to 9.23 p.m. = 8 min
Volume of water that flowed out from 9.15 p.m. to 9.23 p.m.
= 8 x 0.9
= 7.2 ℓ
Volume of water left at 9.23 p.m.
= 13.5 - 7.2
= 6.3 ℓ
Fraction of the tank filled with water at 9.23 p.m.
=
6.327 =
730
Answer(s): (a) 4.5 ℓ; (b) 730