Some psychologists believe that a "genius" should be defined as anyone having an iq over 140. if iq scores are normally distributed with a mean of 100 and a standard deviation of 13, and if the population of the world is 6,575,000,000, how many geniuses are there in the world today?

Hello mate!

if 100 is the mean and 13 is the standard deviation:

(140 - 100)/13 ≈ 3

this means that the value where the geniuses start to appear is equal to the mean plus 3 times the standard deviation.

We know that the percentage that lies after the mean plus 3 times the standard deviation is 0.1% of the population.

Then, if the population is 6,575,000,000

the 1% of this number is equal to:

(1%/100%)*6,575,000,000 = 0.01*6,575,000,000 = 65,750,000

So there are almost 65,750,000 geniuses in the world.

on friday there were 15 birds

thats not a system of equations, that is a solution