Distribution and Z table.

Sunny1982

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Assumming the data is normally distributed and representative of all production estimate the number welds with a strength below 176N, for a production run involving 3000 welds. For quality acceptance less than 0.75% of the welds can be below the 176N, is the process acceptable?.
The Mean is 251.5 and the standard deviation is 29.2532 thanks in advance.

please can someone help me with this question above, my answer for Z= -2.58091 is this correct? if it is how do i look it up on the Z table and what calculations are involved to see if the process is acceptable?
 
Assumming the data is normally distributed and representative of all production estimate the number welds with a strength below 176N, for a production run involving 3000 welds. For quality acceptance less than 0.75% of the welds can be below the 176N, is the process acceptable?.
The Mean is 251.5 and the standard deviation is 29.2532 thanks in advance.

please can someone help me with this question above, my answer for Z= -2.58091 is this correct? if it is how do i look it up on the Z table and what calculations are involved to see if the process is acceptable?
The normal distribution is symmetric about the mean, so they only need to put positive values of z in the table. The probability in the tail below z=-2.58 is equal to the tail above z=+2.58.

Is the probability you get from the table less than 0.75%?

You can multiply the area of the tail [called 1-F(x) in my table] times 3000 to get the expected number of bad welds.
 
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