Answer: she read 1/10 of the book at night.
Explanation:
Let x represent how much of the book that Julie read at night.
Julie read 1/2 of a book in the morning, and she read some more at night. This means that she has read
1/2 + x = (1 + 2x)/2 of the book by night. The portion of the book remaining would be
1 - (1 + 2x)/2 = [2 - (1 + 2x)]/2
= (1 - 2x)/2
By the end of the day, she still had 2/5 of the book left to read. Therefore,
(1 - 2x)/2 = 2/5
Cross multiplying,
5(1 - 2x) = 2 × 2
5 - 10x = 4
10x = 5 - 4 = 1
x = 1/10