Combinatorics

Answer all the questions below and press submit to see how many you got right.

id: 14534

How many of the numbers in 0,1,2,...,999 have a first digit equal to 7?

id: 14462

How many different even numbers smaller than 100 only contain digits between 1 and 9?

id: 14565

How many of the numbers in 1,2,3,...,69 are not divisible by 8?