Junior's box of animal crackers contains ten elephants, ten monkeys, ten zebras, and ten lions. Without looking, Junior grabs one cracker from the box and eats it. What is the probability that both crackers were lions?

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?