Question

Find the indicated IQ score. The graph to the right depicts IQ scores of​ adults, and those scores are normally distributed with a mean of 100 and a standard deviation of 15. with the distribution of 0.75

Answer 1

$$P(X>x)=1-P(Z\le\dfrac{x-\mu}{\sigma})$$

$$=1-P(Z\le\dfrac{x-100}{15})=0.75$$

$$P(Z\le\dfrac{x-100}{15})=0.25$$

$$\dfrac{x-100}{15}\approx-0.6745$$

$$x=89.88$$