a jersey has two digit number.in how many ways can the number be arranged if a)no double digit is allowed b)double digit are allowed​

a) 90

b) 100

Step-by-step explanation:

This is a probability problem. In order to solve it, we must multiply the number of possible numbers by eachother.

a) the first digit can be any number between 0 and 9. That's 10 options. The second digit must be different from the first one: that's 9 options. 10x9=90

b) the first digit can be any number between 0 and 9. That's 10 options. The second digit can also be any number between 0 and 9. That's also 10 options. 10x10=100