Answer: Let's call the rainfall in the second half of the month "x".
From the first half of the month, we know that the total rainfall was 1/5 inch.
At the end of the month, we know that the total rainfall was 1/2 inch:
1/5 + x = 1/2
Subtracting 1/5 from both sides:
x = 1/2 - 1/5
x = 3/10
So the rainfall in the second half of the month was 3/10 of an inch.
Explanation: