折线图显示了下午 1 点到下午 5 点水箱中的水量。下午 1 点时，水箱里装了 20% 的水。从下午 1 点到下午 5 点，水流入了水箱。

1. Read the volume of water at each hour from the graph

At 1 p.m.: $6$ litres
At 2 p.m.: $12$ litres
At 3 p.m.: $20$ litres
At 4 p.m.: $25$ litres
At 5 p.m.: $28$ litres

2. Calculate the flow (increase in volume) for each 1-hour interval

1 p.m. to 2 p.m.: $12 - 6 = 6$ litres
2 p.m. to 3 p.m.: $20 - 12 = 8$ litres
3 p.m. to 4 p.m.: $25 - 20 = 5$ litres
4 p.m. to 5 p.m.: $28 - 25 = 3$ litres

3. Identify the interval with the greatest flow

The greatest increase is $8$ litres, which occurred from 2 p.m. to 3 p.m.

1. Find the total capacity of the tank using the data at 1 p.m.

At 1 p.m., the volume of water is $6$ litres, which corresponds to $20\%$ of the tank.
$20\% \rightarrow 6 \text{ litres}$
$100\% \rightarrow 6 \times 5 = 30 \text{ litres}$
The total capacity of the tank is $30$ litres.

2. Calculate the fraction of the tank filled at 5 p.m.

At 5 p.m., the volume of water is $28$ litres.
Fraction of tank filled = $\frac{28}{30} = \frac{14}{15}$