Question

How much money does a typical family spend at McDonald’s per visit ? The amount is a normally distributed random variable with mean $ 17,9 and standard deviation $3,55. What is the amount below which only 10% of families spend at McDonald’s ?

Answer 1

$P(Z<z)=0.1\to z=-1.28.$

$\frac{x-17.9}{3.55}=-1.28.$

$z=17.9-1.28*3.55=13.36.$

The amount below which only 10% of families spend at McDonald’s is $13.36.