Dori spent 1/5 of her money on a toy boat and scuba goggles. The toy boat cost 2 times as much as the goggles. The toy boat cost $8. How much money does Dori have left?​

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?