Question

A school principal claims that grade 11 students have a mean grade of 86 with a standard deviation of 4. suppose that the distribution is approximately normal. What is the probability that a random selected grade will be less than 84?

Answer 1

$$P(X<84)=P(Z<\dfrac{84-86}{4})$$

$$=P(Z<-0.5)\approx0.3085$$