Question

The probability that a randomly selected individual in a certain community has made an online purchase is 0.41 . Suppose that a sample of 13 people from the community is selected, what is the probability that at most 3 of them has made an online purchase?

Write only a number as your answer. Round to 2 decimal places (for example 0.24). Do not write as a percentage.

Answer 1

0.15

Explanation:

What we can use to solve this problem is the Bernoulli approximation of the Binomial distribution.

When we say at most 3, it means 0 or 1 or 2 or 3 people out of the 13 made the purchase

Mathematically, the Bernoulli approximation is applied as follows

P(X = n) = nCr p^r q^n-r

let p = probability of making online purchase = 0.41

while q = 1-p = 1-0.41 = 0.59 which is the probability of not making an online purchase.

Mathematically for each of the approximations up to 3, we have ;

13C0 P^0 q^13 + 13C1 P^1 q^12 + 13C2 P^2 q^11 + 13C3 P^3 q^10

Making substitutions, we have

{1 * 0.41^0 * 0.59^13} + {13 * 0.41^1 * 0.59^12} + {78 * 0.41^2 * 0.59^11} + {286 * 0.41^3 * 0.59^10}

= 0.150820944904 which is 0.15 to 2 decimal places