Question

If rob flips 3 coins what is the chance that they come up all tails

Answer 1

One way you could solve this would be to write out all the possible ways the 3 coins could land. There are 8 different arrangements.

H-H-H
H-H-T
H-T-H
H-T-T
T-T-T
T-T-H
T-H-H

You can see that there is 1 possible way that the coins give you the result you asked for; three tails. So that's 1 out of 8.. 1/8 = 0.125 = 12.5%

Answer 2

1/8. 1/2*1/2*1/2 = 1/8. Each 1/2 represents the probability of getting tails on each flip. We multiply three of them because there are three flips.