Question

Please Help! I'll medal and favorite!

Suppose there are 21 students in your class. If the teacher draws 2 names at random, what is the probability that you and your best friend will be chosen?

A: 2/21
B: 1/20
C: 1/105
D: 1/210

Answer 1

The probability of you being chosen is 1/21 (desired outcomes/possible outcomes) and 1/20 for your best friend, since you can't be chosen twice. The probability of two independent events occurring is the product of their individual probabilities, so the overall probability would be (1/21)*(1/20)=1/420. I'm not sure why that's not an option; I'm fairly certain that's the answer.

Answer 2

Another way to think of it in terms of permutations/combinations (if you've done that) is 21 nPr 2

Answer 3

Thanks!