# Thread: Is my thinking correct?

1. ## Is my thinking correct?

I actually figured this one out ( it took 15 minutes, which is good for me) but need to clarify the answer as the text does not provide it!

The probability that a person has immunity to a particular disease is 0.1. Randomly select 5 people from the population. Find the probability that among the 5 people selected:
a) exactly 1 person have immunity to the disease
b) at most 1 person have immunity to the disease.

For "A" I use n = 5, p=0.1 and j= 1
using the nCjpj(1-p)n-j formula I worked it out to be .33

For"B" I used 1 - .33

Am I correct?

2. Karen,

A is correct.

For B, "exactly 1" and "at most 1" aren't complements.

"at most 1" is the same as "zero OR one" also written as "zero + one" so you need to find P( j = zero ), using the same method as in A, then add it to your answer in A.

John

3. It makes sense now! thank you.

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts