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 3.9 litres per minute. After 7 minutes, tap B was turned on. At 9.11 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 35 x 20
= 42000 mℓ
= 42 ℓ
Volume of the tank at 9.11 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
= 11 - 7
= 4 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 4 min
= 27.3 - 21
= 6.3 ℓ
Volume of water that flowed out in 1 min
= 6.3 ÷ 4
= 1.575 ℓ
Volume of water that flowed out of Tap B in 1 min
= 3.9 + 1.575
= 5.475 ℓ
(b)
Duration from 9.11 p.m. to 9.23 p.m. = 12 min
Volume of water that flowed out from 9.11 p.m. to 9.23 p.m.
= 12 x 1.575
= 18.9 ℓ
Volume of water left at 9.23 p.m.
= 21 - 18.9
= 2.1 ℓ
Fraction of the tank filled with water at 9.23 p.m.
=
2.142 =
120
Answer(s): (a) 5.475 ℓ; (b) 120