If a person is healthy. he has a chance of being greater than years old. If a person is greater than years old, he has an chance of being healthy. Suppose of the citizens in a city are greater than 70 years old. What is the probability that a randomly selected person is healthy? Correct to significant figures.
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Let P be the population
Above 70 yrs = 0.15*P
Out of this, healthy = 0.15* 0.85 * P -------- (1)
Let N be healthy
Above 70 yrs = 0.2*N ---------------------- (2)
From (1) and (2), 0.15* 0.85 * P = 0.2*N ------ (3)
Probability that a randomly selected person is healthy = N/P
Using (3), we have N/P = 0.15*0.85/0.2 = 0.6375