please help

[kim270]

Intelligence Quotient (IQ) scores are approximately normally distributed with mean 100 and varience 400

suppose that a sample of 500 individuals is selected, find an approximation to the probability that the number of sampled people with an IQ of higher than 120 is between 60 and 90 (inclusive of both 60 and 90)

can some point in the direction in the direction to begin this question please

 

[Lizzie]

I think you may need to be a bit more specific.

 

[tkhunny]

Intelligence Quotient (IQ) scores are approximately normally distributed with mean 100 and varience 400

suppose that a sample of 500 individuals is selected, find an approximation to the probability that the number of sampled people with an IQ of higher than 120 is between 60 and 90 (inclusive of both 60 and 90)

can some point in the direction in the direction to begin this question please

Simple z-score. z = (120-100)/sqrt(400) = 1, z = (60-100)/sqrt(400) = -2, z = (90-100)/sqrt(400) = -½ What kind of probabilities hang around that many standard deviations?

Note: It's a continuous distribution with no mass. Including or excluding the end points makes no difference.