Sudoku, KenKen, and more
Three friends share a $30 hotel room (each pays $10). The clerk realizes the room costs only $25 and gives $5 back. The bellhop keeps $2 for himself and returns $1 to each person. So each person paid $9 (total: $27) and the bellhop has $2. Where's the missing dollar?
I have as many brothers as sisters. But each of my sisters has twice as many brothers as sisters. How many boys and girls are in my family?
Using six 9s and any math operations (+, -, ×, ÷, parentheses), make 100.
How many seconds are in a year? (No calculator!)
How many people do you need in a room before there's a 50% chance two of them share a birthday?