Suppose we want to choose 2 colors, without replacement, from the 3 colors red, blue, and green. (a) How many ways can this be done, if the order of the choices is relevant? X (b) How many ways can this be done, if the order of the choices is not relevant? ​

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?