Question

A bike lock has a 4 digit combination. Each character can be any digit between 1-9. The only restriction is that all 4 character cannot be the same(e.g. 1111, 2222, 3333... etc). How many combinations are possible?

a. 6552
b. 6561
c. 9990
d. 10000

Answer 1

Answer:

c. 9990

Step-by-step explanation:

there are 9999 4-digit numbers

1111

2222

3333

4444 and so on are only nine 4-digit number

so, 9999-9=9990