Combinatorics

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

id: 14520

How many of the numbers in 0,1,2,...,999 have at least one digit equal to 9?

id: 14458

How many different even numbers smaller than 100 only contain digits between 1 and 5?

id: 14613

In a restaurant the guests can choose a main out of 10 pizzas and 4 pastas. How many main courses are there?