Martha types a 4−digit code into a keypad to unlock her car doors. The code uses the numbers 1 and 0. If the digits are selected at random, what is the probability of getting a code with exactly three 0's?
We have 2^4 = 16 possible codes
Codes with three 0s
0001
0010
0100
1000
So....the probability is 4 / 16 = 1 / 4
