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# The probability that a person is immune to a certain disease

### Resolved Question:

The probability that a person is immune to a certain disease is 0.40.
a. What si the probabilty that 4 people will have the disease in a sample of 12 people?
b. Find the mean number of people who have immunity in a sample of size 12.
c. Find the standard deviation for the same sample.
Submitted: 5 years ago.
Category: Math Homework
Expert:  Scott replied 5 years ago.

Hi there,

The probability that a person is immune to a certain disease is 0.40.
a. What si the probabilty that 4 people will have the disease in a sample of 12 people?
= 12 choose 4 * 0.4^4 * 0.6^8
= 495 * 0.4^4 * 0.6^8
= 0.21284093952

b. Find the mean number of people who have immunity in a sample of size 12.
= np
= 12*0.4
= 4.8

c. Find the standard deviation for the same sample.
= sqrt(nqp)
= sqrt(12*0.4*0.6)
= 1.697056

Let me know if you have any questions,
Scott