Aperson wishes to mix coffee worth $9 per lb with coffee worth $3 per lb to get 240 lb of a mixture worth $5 per lb. how many pounds of the $9 and the $3 coffees will be needed?

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?