Final answer:
The percentage change in rainfall between March and April is a 20% fall.
Step-by-step explanation:
To find the percentage change in rainfall between March and April, we need to calculate the difference and express it as a percentage of the initial value.
The initial rainfall in March was 85 mm and the rainfall in April was 68 mm. The difference is 85 - 68 = 17 mm.
To find the percentage change, divide the difference by the initial value and multiply by 100:
(17 / 85) * 100 = 20%
Therefore, the percentage change in rainfall is a 20% fall.