PSLE
At first, ²₉ of a tank was filled with water. A tap was turned on for 40 min for more water to flow into the tank. It was then turned off. The line graph shows the volume of water in the tank over the 40 min.

1. How many litres of water flowed into the tank in one minute?
2. At the end of 40 min, what fraction of the tank was filled with water?
3. The tap was turned on again to fill up the tank at the same rate as before. How many more minutes did it take for the tank to be filled completely?

(a)
Volume of water that flowed into the tank from the tap in 5 min
= 200 - 160
= 40 ℓ

Volume of water that flowed into the tank in one minute
= 40 ÷ 5
= 8 ℓ

(b)
Capacity of the tank
= 160 ÷ ²₉ 
= 160 x ⁹₂
= 720 ℓ

Fraction of the tank that was filled with water
= ²₃

(c)
Fraction of the tank to be filled
= 1 - ²₃
= ¹₃

Remaining volume of the tank to be filled
= ¹₃ x 720
= 240 ℓ

Remaining time needed for the tank to be filled completely
= 240 ÷ 8
= 30 min

Answer(s): (a) 8 ℓ; (b) ²₃; (c) 30 min