Chris read 1 / 4 of a book in the morning, and he read some more at night. By the end of the day, he still had 1 / 3 of the book left to read. How much of the book did Chris read at night?

Answer: Chris read 5/12 of the book at night.

Step-by-step explanation:

Let 1 represent the volume or size of the full book.

Chris read 1/4 of a book in the morning.

He read some more at night.

Let x represent the size that he read at night. This means that he read x/1 = x at night

Total volume or size of the book that he has read is 1/4 + x

The volume or size of the book left to read is

1 - (1/4+x)

By the end of the day, he still had 1 / 3 of the book left to read. This means that

1 - (1/4+x) = 1/3

1 - 1/4 - x = 1/3

Multiplying through by 12

12 - 3 - 12x = 4

12x = 12 - 3 - 4

12x = 5

x = 5/12

5/12

Step-by-step explanation:

1/4 (what he already read) = 3/12

1/3 (what he had left) = 4/12

12/12 (whole book) - 4/12 (what he has left to read) = 8/12 (what he already read+what he read during the day)

8/12 - 3/12 (what he already read) = 5/12 (what he read during the day)

answer: 5/12