Lizzy: The price of a math textbook in the school bookshop is $45. If those sold in bookshops outside the school cost 20% less, how much can Peter save by buying from other bookshops rather than the school's if he wants to buy 3 math textbooks?.
Me: Hmmm, let me think. I think this is the detailed solution:
20% of $45 is (20 / 100) * $45 = $9. The price of the textbook in other bookshops cost $9 less than $45 which is $45 - $9 = $36. Three textbooks from the school bookshop would cost $45 * 3 = $135. Three textbooks from another bookshop would cost $36 * 3 = $108. Peter can save $135 - $108 = $27 by buying from another bookshop. Final answer: 27.