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0.65/own cell phone under 18 NOT own cell phone 0.25 own cell 0.79phone 0.45 18-

ID: 2949649 • Letter: 0

Question

0.65/own cell phone under 18 NOT own cell phone 0.25 own cell 0.79phone 0.45 18-65 NOT own cell phone own cell 0.44' phone over 65 NOT own cell phone A population consist of 25% under the age of 18, 45% in age of 18 to 65 and the rest over the age of 65. In the age group 18 and under 65% own a cell phone, while in the 18 to 65 group 79% own a cell phone . The over the age of 65 group 44% own a cell phone. Suppose we choose a person from this population that owns a cell phone. What is the probability that this person is under 18? Write your answer as the exact decimal if the number is less than or equal to the ten- thousandths place, or round to the ten-thousandths place if the decimal is longer.

Explanation / Answer

Bayes' Theorem: P(A | B) = P(A and B)/ P(B)

P(over 65) = 1 - 0.25 + 0.45

= 0.30

P(under 18 | own cell phone) = P(under 18 and own cell phone) / P(own cell phone)

= (0.25 x 0.65) / (0.25x0.65 + 0.45x0.79 + 0.30x0.44)

= 0.1625/0.65

= 0.25