Question 455:

Asked on October 4, 2008

Tags: Quartile

1

Answer:

No answer provided yet.

We need to find the z-score for the 25th percentile. We can use the percentile to z-score calculator using the 1-sided area. This will provide us with the z-score corresponding to 25% of the area under the curve. Enter .25 and you should get a z-score of -0.675. Now we just setup an equation and solve for the unknonw IQ. The equation for a z-score is (x-mean)/standard deviation.

1. (x-10)/2 = -0.675
2. x-10 = -1.35
3. x = 8.65

So an IQ of 8.65 represents the 25th percentile given the mean of 10 and sd of 2. 75% of IQ scores would be above 8.65.