We obtain the probabilities by dividing the frequencies by the total number N of times the experiment was conducted (the sum of the frequencies). The frequencies add up to N = 3 + 12 + 20 + 10 + 5 = 50. Dividing each of the frequencies by N gives the corresponding probability:

x	50	150	250	350	450
Frequency	3	12	20	10	5
P(X = x)	3 50 = .06	12 50 = .24	20 50 = .40	10 50 = .20	5 50 = .10

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