Antonio planned to read 15books over the summer for the library summer reading challenge. At the end of July he had read 4/5 of books how many books had he read?

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.