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 4.5 litres per minute. After 8 minutes, tap B was turned on. At 3.10 p.m., the tank was half filled with water.
- How many litres of water flowed out of tap B in 1 minute?
- At 3.21 p.m., what fraction of the tank was filled with water?
(a)
Volume of the tank
= 60 x 35 x 30
= 63000 mℓ
= 63 ℓ
Volume of the tank at 3.10 p.m. when it was half filled with water
= 63 ÷ 2
= 31.5 ℓ
Volume of water by Tap A for 8 min
= 8 x 4.5
= 36 ℓ
Duration that Tap B was turned
= 10 - 8
= 2 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 2 min
= 36 - 31.5
= 4.5 ℓ
Volume of water that flowed out in 1 min
= 4.5 ÷ 2
= 2.25 ℓ
Volume of water that flowed out of Tap B in 1 min
= 4.5 + 2.25
= 6.75 ℓ
(b)
Duration from 3.10 p.m. to 3.21 p.m. = 11 min
Volume of water that flowed out from 3.10 p.m. to 3.21 p.m.
= 11 x 2.25
= 24.75 ℓ
Volume of water left at 3.21 p.m.
= 31.5 - 24.75
= 6.75 ℓ
Fraction of the tank filled with water at 3.21 p.m.
=
6.7563 =
328
Answer(s): (a) 6.75 ℓ; (b) 328