You randomly draw a marble from a bag, record its color, and then replace it. You draw a red marble 3 out of 20 times. What is the experimental probability that the next marble will be red?

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?