BTGModeratorVI wrote: ↑Mon Apr 13, 2020 3:39 pm
A men's basketball league assigns every player a two-digit number for the back of his jersey. If the league uses only the digits 1-5, what is the maximum number of players that can join the league such that no player has a number with a repeated digit (e.g. 22), and no two players have the same number?
A. 20
B. 21
C. 22
D. 24
E. 25
Answer:
A
Source: Manhattan prep
Solution:
We need to determine how many two-digit numbers can be created from 5 digits (1 to 5, inclusive), with no repeated digits. Since order matters, we have a permutation. Thus, the number of ways to create two-digit numbers is 5P2 = 5!/(5 - 2)! = 5 x 4 = 20.
Alternate Solution:
If repeated digits were allowed, there would be 25 possibilities since, for each digit, we would have 5 choices. Among these 25 possibilities, 5 of them are repeated digit numbers (which are 11, 22, 33, 44, and 55). Thus, without the repeated digits, there are 25 - 5 = 20 numbers possible.
Answer: A
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