PSLE The figure shows taps A and B and an empty tank. At 8 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 8.11 p.m., the tank was half filled with water.
- How many litres of water flowed out of tap B in 1 minute?
- At 8.21 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 8.11 p.m. when it was half filled with water
= 60 ÷ 2
= 30 ℓ
Volume of water by Tap A for 8 min
= 8 x 4.2
= 33.6 ℓ
Duration that Tap B was turned
= 11 - 8
= 3 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 3 min
= 33.6 - 30
= 3.6 ℓ
Volume of water that flowed out in 1 min
= 3.6 ÷ 3
= 1.2 ℓ
Volume of water that flowed out of Tap B in 1 min
= 4.2 + 1.2
= 5.4 ℓ
(b)
Duration from 8.11 p.m. to 8.21 p.m. = 10 min
Volume of water that flowed out from 8.11 p.m. to 8.21 p.m.
= 10 x 1.2
= 12 ℓ
Volume of water left at 8.21 p.m.
= 30 - 12
= 18 ℓ
Fraction of the tank filled with water at 8.21 p.m.
=
1860 =
310
Answer(s): (a) 5.4 ℓ; (b) 310