A bookshop has an offer. "Buy one book and get one free!"
Ria gets 8 books from the shop with that offer.
The normal price of each book is £5.99.
How much does Ria spend?

You are standing next to a really big circular lake. you want to measure the diameter of the lake, but you don't want to have to swim across with a measuring tape! you decide to walk around the perimeter of the lake and measure its circumference, and find that it's 400\pi\text{ m}400? m. what is the diameter dd of the lake?