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Probability is a number that says how likely something is, and it is always written as a fraction built the same way: the number of outcomes you want on top, the total number of outcomes on the bottom.
In a bag with 3 red, 5 blue, and 2 green marbles, the total is 10, so the probability of drawing red is 3 over 10.
If the question uses the word not, count everything that does not match and put that count on top. Not red would be 7 out of 10.
The part to read carefully is the beginning of the question, because it names your group. "A student is picked at random" means the group is everyone. "A junior is picked" means the group is only the juniors, so the junior total goes on the bottom.
Reduce your fraction at the end. Every probability lands between 0 and 1.
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