Combinatorics › Pigeonhole and extremal problems › Coloured beads and balloons
Red 4-door cars in a parking lot
Middle school · ●○○○○ 10 pts
There are 20 cars in a parking lot. All of the cars are red or white, and all of the cars are either 2-door or 4-door. Of these cars, 12 are red, 15 are 4-door, and 4 are 2-door and white. How many of the cars are 4-door and red?