Upper Quartile & Lower Quartile

• May 2nd 2009, 07:45 PM
brumby_3
Upper Quartile & Lower Quartile
The distribution of the birth weights of babies delivered at 40 weeks is approximately normal with a mean of 3500g and standard deviation of 430g.

Calculate the upper quartile of birth weight. What is the lower quartile?
• May 2nd 2009, 10:30 PM
mr fantastic
Quote:

Originally Posted by brumby_3
The distribution of the birth weights of babies delivered at 40 weeks is approximately normal with a mean of 3500g and standard deviation of 430g.

Calculate the upper quartile of birth weight. What is the lower quartile?

Upper quartile:

You need to solve Pr(X > x) = 0.25 for x.

To do this, first find the value of z* such that Pr(Z > z*) = 0.25.

Now note that $z* = \frac{x - 3500}{430}$ and solve for x.

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Lower quartile is done the same way.