Question

Credit cards place a three digit security code on the back of cards. What is the probability that a code starts with the number 7?

Answer 1

The probability that a code starts with the number 7 is:

1/10

Explanation:

There are total 10 digits:

0 1 2 3 4 5 6 7 8 9

Also, the total number of codes that are possible using these digits are:

1000

( Since there are 10 choices for first place, 10 for second and 10 for third as well

Hence, total possibilities are: 10×10×10=1000 )

Also, if the first place of the code is fixed with number 7.

So, we need to chose the digits for second and third place.

Hence, total codes whose first digit is 7 are:

100

( Since the choice for first place is fixed and for second and third place we have 10 choices i.e. total such cases are: 1×10×10=100 )

Hence, the probability is calculated as:

Probability=100/1000

=1/10