Statistics Problem

[sexysummer]

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The average IQ of the city of Gotham is 110, and the standard deviation is 15.
If the city has a population of 15,000, what would be a reasonable number of
people whose IQ is above 140?

The solution is given but I don't understand the explanation.

Thank you

 

[NavyDDS1990]

each standard deviation is 15 and it is asking people with IQ of 140 above, which is 2 standard deviations away from 110.
By the 68-95-99.7 rule, 5% of the population will be 2 standard deviations away, then you do 0.05 * 15,000 = 750 people.
total 750 people are 2 standard deviations away, so you divide that by 2 you get total number of people with IQ of 140 above, which is 375