Hi,

"7% of al switches produced are defective. if 200 switches are selected at random, 

what us the probability that more than 20 will be defective?" 

BINOMIAL Distribution P(x) = nCx*  

where p and q are the probabilities of success and failure respectively. 

In this case p = .07 & q = .93 & n = 200   nCx = 

 P(20) =(200C20)(.07)^20(.93)^180   Or binompdf(200, .07, 20)on calculator

Recommend using Your TI calculator for cumulative probabilities

and/or stattrek.com as an excellent reference.  

 P(x>20) = 1 - P(x ≤ 20)  = 1 - binomcdf(200, .07, 20) on a Ti calculator

Without a Calculator: 1 - [ P(0) + P(1) + P(2) .... + P(20)]

Tedious, but can be done.

Again: stattrek.com is an excellent reference (also has calculators)

 

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