PSLE The figure shows taps A and B and an empty tank. At 10 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 7 minutes, tap B was turned on. At 10.12 p.m., the tank was half filled with water.
- How many litres of water flowed out of tap B in 1 minute?
- At 10.26 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 10.12 p.m. when it was half filled with water
= 42 ÷ 2
= 21 ℓ
Volume of water by Tap A for 7 min
= 7 x 3.9
= 27.3 ℓ
Duration that Tap B was turned
= 12 - 7
= 5 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 5 min
= 27.3 - 21
= 6.3 ℓ
Volume of water that flowed out in 1 min
= 6.3 ÷ 5
= 1.26 ℓ
Volume of water that flowed out of Tap B in 1 min
= 3.9 + 1.26
= 5.16 ℓ
(b)
Duration from 10.12 p.m. to 10.26 p.m. = 14 min
Volume of water that flowed out from 10.12 p.m. to 10.26 p.m.
= 14 x 1.26
= 17.64 ℓ
Volume of water left at 10.26 p.m.
= 21 - 17.64
= 3.36 ℓ
Fraction of the tank filled with water at 10.26 p.m.
=
3.3642 =
225
Answer(s): (a) 5.16 ℓ; (b) 225