PSLE
At first, ¹₁₂ of a tank was filled with water. A tap was turned on for 30 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 30 min.

1. How many litres of water flowed into the tank in one minute?
2. At the end of 30 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 - 100
= 100 ℓ

Volume of water that flowed into the tank in one minute
= 100 ÷ 5
= 20 ℓ

(b)
Capacity of the tank
= 12 x 100 
= 1200 ℓ

Fraction of the tank that was filled with water
= ⁷⁰⁰₁₂₀₀
= ⁷₁₂

(c)
Fraction of the tank to be filled
= 1 - ⁷₁₂
= ⁵₁₂

Remaining volume of the tank to be filled
= ⁵₁₂ x 1200
= 500 ℓ

Remaining time needed for the tank to be filled completely
= 500 ÷ 20
= 25 min

Answer(s): (a) 20 ℓ; (b) ⁷₁₂; (c) 25 min