The length of a screw produced by a machine is normally distributed with a mean of 0.65 inches and a standard deviation of 0.01 inches. What percent of screws are between 0.61 and 0.69 inches?

65%

68%

99.7%

100%

Question

The length of a screw produced by a machine is normally distributed with a mean of 0.65 inches and a standard deviation of 0.01 inches. What percent of screws are between 0.61 and 0.69 inches?

65%

 68%

 99.7%

 100%

anonymous · Answer

D. 100%
The deviation of 0.01 inches means that the screw will always be between 0.64 inches and 0.66 inches.

amistre64 · Answer

the average deviation does not imply that its the only deviation of a mesurement

amistre64 · Answer

but id agree that 4 standard deviations from the mean is highly unlikely to happen; the thing is, how accurate do you need the results?

amistre64 · Answer

if anything, we can run a normal cumulative distribution function with the information given as: normalcdf(low, high, mean, sd) http://www.wolframalpha.com/input/?i=normalcdf%28.61%2C+.69%2C+.65%2C.01%29 which gives us practically 0% in each tail

anonymous · Answer

I don't know, they give options of percents so that's all I need I guess. Would it be 100%?

amistre64 · Answer

since 61 and 69 are both 4(1) from the mean, then yeah ... the probability of being outside of that range is .00006, which approximates to 100% in my view

anonymous · Answer

Thanks! Can you help with this one?:

The probability that a train leaves on time is 0.8. The probability that the train arrives on time and leaves on time is 0.24. What is the probability that the train arrives on time, given that it leaves on time?

 0.3

 0.8

 0.16

 0.24