How Likely Is That? Page 3 Shelly Berman shelly@mathforum.org Page 1 || Page 2 || Page 3 || Page 4 Probability Experiments Experiment 1 If you toss a single number cube (one die), what is the probability of rolling an even number? One way of thinking about probability is to make a fraction that shows: (the number of things you want) (the number of possibilities). How many different numbers could you get when you roll a number cube? How many of these are even? When you roll a number cube you can get any of the six numbers: 1, 2, 3, 4, 5, or 6. Three of these numbers are even: 2, 4, and 6. That is, the probability of rolling an even number can be written as: P(even number) = (3 numbers we want)/(6 possible numbers) = (3/6). So, the probability of rolling an even number on a number cube is (3/6). Where is this on the probability scale from 0 to 1? How do you know? Experiment 2 How do you think we could measure the probability of tossing a die and getting a 1? Is it more likely that you will get a 1 or that you won't get a 1? In fact, can you measure the probability of tossing a die and getting any number but a 1? Experiment 3 Here's a set of twenty cards. Each card has a number from 1 to 10, and the number is either red or black. If I draw one card without looking, what is the probability that the card I draw will: be red? show an even number? show a number less than 3? show a black 7? Can you think another outcome from drawing one card that has a probability of: (1/2)? (1/4)? (4/20)? (1/20)? (19/20)?

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