Canadian postal codes are of the form "letter number letter number letter number," such as K2N 3P8. In the province of Ontario all postal codes must begin with K, L, M, N, or P. How many postal codes are possible for Ontario?

A passcode for a secure website has 6 digits. The first digit cannot be 0. The final 6-digit passcode must be an even number. No digit can be repeated. How many different passcodes are possible? Include evidence of your work by typing out your full solution.

Suppose the city of MISSISSAUGA has a contest where they arrange the letters of their city name in a particular order. The city residents have to guess which order the city has chosen, and the winner gets $10 000. The rules allow people to submit more than one entry, but they each have to be mailed individually. A friend of yours wants to mail every possible entry to be guaranteed to win the $10 000. Use a mathematical argument to explain to your friend why this isn't a good idea.

A family has 3 boys and 5 girls. How many of these teams of 5 will contain at least 3 girls? Use the indirect approach to find the answer.