Question

Suppose the same quantity is measured but with a more precise method giving an average and standard deviation of 15.0 ± 2.5. how many students out of 100 would you now expect to get a measurement greater than 20?

Answer 1

To solve this, we use the z test.

The formula:

z = (x – u) / s

where x is sample value = 20, u is the mean = 15, and s is the standard deviation = 2.5

z = (20 – 15) / 2.5

z = 2

Since we are looking for values greater than 20, this is right tailed test. We use the standard distribution tables to find for P.

P = 0.0228

 

Therefore:

number of students = 100 * 0.0228 = 2.28

 

2 to 3 students will get greater than 20 measurement