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March 2, 2015

March 2, 2015

Posted by **Joy** on Sunday, January 22, 2012 at 4:14pm.

9.0 months 7.0 months

8.2 months 8.3 months

7.8 months 8.1 months

7.5 months 7.6 months

9.1 months 7.4 months

I calculated the standard deviation to be about 0.679.

Estimate the probability that a random chosen light will last as long as 7 months after installation. Assume the data to be described by a normal distribution.

Can anyone help me with the process I would use to calculate the answer? Thanks!

- Statistics -
**MathGuru**, Sunday, January 22, 2012 at 7:31pmUse z-scores. Find the mean. You have already calculated standard deviation.

Formula for z-scores is the following:

z = (x - mean)/sd

Use 7 for x. Calculate z-score. Determine the probability using a z-distribution table.

- Statistics -
**Joy**, Sunday, January 22, 2012 at 7:42pmThanks for the insight!

So I've calculated the z-score to be about -1.47, or about -1.5. Looking at a z-distribution table, I see on the left a column for z-scores and I see -1.5 there, but there are many values corresponding on the right?

Do you know how I know which one to use?

- Statistics -
**Joy**, Sunday, January 22, 2012 at 7:58pmNever mind- I've figured it out, THANK YOU MathGuru!

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