Answer:
He had read 12 books.
Explanation:
Let us first rewrite the main information from the task.
He planned to read 15 books.
He had read 4/5 so far.
How many books is that?
This basically means that we have to calculate how much is 4/5 of 15.
The easiest way to do this is to multiply 4/5 and 15.
Let's mark with x the number of the books he had read:
x = 4/5 • 15
x = 12
We cat think of this as splitting 15 into five equal parts, and then taking four of those parts. Each part will be 15 / 5 = 3, so four parts will be 4 • 3 = 12.
