Elmentary Math for Teachers II
posted by Tracy .
In a class of seven students, a teacher spins a sevensectored spinner (with equalsized sectors) to determine which students to ask questions. Determine about how many times a student can expect to be called on when 100 questions are asked.

1/7 of the 100 questions, or 1415 times.

From a set of eight marbles, five red and three white, we choose one at random. What are the odds in favor of choosing a red marble?

same kind of idea. Think of a spinner which is 5/8 red and 3/8 white. If you spin it, you will likely hit red 5/8 of the time.
Looking at the marbles, 5 of the 8 are red, so if you grab one, it will probably be red (5/8 of the time)