A cat has a litter of six kittens. You plan to adopt 2 of the kittens. In how many ways can you choose 2 of the kittens from the litter?

There are 6 kittens when you're deciding which one you want to pick, so there are 6 ways of chosing one. Then, the number of kittens lowers to 5, so there are 5 ways of picking another. At all, there are 30 ways of chosing 2 kittens out of 6.