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A compact disc is designed to last an average of 4 years with a standard deviation of 0.9 years. What is the probability that a CD will last less than 3 years? 1.11% 13.35% 86.65% 100%
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A compact disc is designed to last an average of 4 years with a standard deviation of 0.9 years. What is the probability that a CD will last less than 3 years?

1.11%
13.35%
86.65%
100%

User WordCent
by
7.8k points

1 Answer

2 votes
3 is 1.0 below the mean. That is 1.0 / 0.9, or 1.1111... standard deviations below the mean.
So look up z < -1.11 on your graphing calculator.
It should be around 0.1335 or 13.35%
User Matt McManis
by
8.1k points
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