Question

In a normal distribution, the standard deviation is 20, what test score do you need to be in the top 2.5%? please help no mean is given if there was one i wouldn't ask

Answer 1

Answer)

As the data is normally distributed we can use standard normal z table to estimate the answers

Z = (x-mean)/s.d

Given s.d = 20

From z table, P(z>1.96) = 2.5%

So, z = 1.96

1.96 = (x - mean)/20

X = mean + 1.96*20

Or we can say that test score to be in top 2.5 is 1.96 standard deviation above the mean