Help PLEASE, I don't understand

Question

Assume that adults have IQ scores that are normally distributed with a mean of

mu equals μ=105 and a standard deviation

sigma equals σ=20.

Find the probability that a randomly selected adult has an IQ less than

145.

Answer 1

145-105=40=2 standard deviations from the mean.

Use the 68-95-98 rule. 95% of adult IQ's are within 2 standard deviations from the mean

with 5% that aren't split in half, so that 2.5% are above 145

and the other half that aren't are 2.5% below 105-40 or 65

Answer is 100%-2.5%=97.5% IF 2.5% are above 145, then 100% minus 2.5% are below 145.