Statistics question-please explain? (10 points!)?

Question

"Smith is a weld inspector at a shipyard. He knows from keeping track of good and substandard welds that for the afternoon shift 5% of all welds done will be substandard. If smith checks 300 of the 7500 welds completed that shift, what is the probability that he will find more than 25 substandard welds?"A) .4960B) .5040C) .0040 D) .9960....I have no idea how to work this problem. Can someone please explain to me how to? PLEASE...

Dr. Karlee Tillman · Accepted Answer

Probability of finding a substandard weld = p = 5% = 0.05Sample size = n= 300 According to Poisson Distributionthe average number of welds= m = np = 300 0.05 =15the stadard deviation of welds = Square root of m = sqrt of 15 = 3.873By using Normal distribution, z value corresponding to 25 is to be calculatedz =( X - Mean) / standard deviation =(25 - 15) / 3.873 = 10 / 3.873 = 2.58According to the Area under Stadard Normal Curve tablesArea right to z=2.58 is to be locatedIt comes to 0.0040 approximatelySo the probability of finding more than 25 substandard welds = 0.0040The answer to the question is (c)

Dr. Karlee Tillman · Answer

Smith is a weld inspector at a shipyard. Heknows from keeping track of good andsubstandard welds that for the afternoon shift5% of all welds done will be substandard. IfSmith checks 300 of the 7500 welds completedthat shift, what is the probability that he willfind less than 20 substandard welds?

Alize Kuhn

Statistics question-please explain? (10 points!)?

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