Alan buys a book that is on sale. He writes the expression 0.7b to show the percent of the original cost of the book, b, that he pays.
He rewrites the expression as b−0.3b.
Which statement explains why Alan rewrites the expression?

He receives another discount on the book.

He buys another book with a different discount.

He wants to show by what percent the book was discounted.

He wants to show what percent of the original price he paid.