Posted by **Anonymous** on Friday, February 28, 2014 at 7:49pm.

Statistics show that about 5% of all males are colorblind. Suppose that 20 males are selected at random.

What is the probability that at least 4 of the 20 people are colorblind?

My answer: I got 1-0.984

The answer key says 0.00257394

- Probability -
**Reiny**, Friday, February 28, 2014 at 9:00pm
at least 4 means

4 or 5 or 6 or ... or 20 are colourblind

so exclude cases of none, 1 , 2, and 3

colourblind = .05

not colourblind = .95

None:

C(20,0) (.05)^0 (.95)^20 = .358486

one:

C(20,1) (.05) (.95)^19 = .37735..

two:

C(20,2) (.05)^2 (.95)^18 = .1886768

three:

C(20,3)(.05)^3 (.95)^17 = .059582..

adding up those 4 and subtracting from 1 I got .0159

which is the same result as you had

mmmhhhh?

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