The question is missing alternatives. The complete question is here.
For each student in a certain class, a teacher adjusted the student's test score using the formula y = 0.8x + 20, where x is the student's original test score and y is the student's adjusted test score. If the standard deviation of the original test scores of the students in the class was 20, what was the standard deviation of the adjusted test scores of the students in the class?
A. 12
B. 16
C. 28
D. 36
E. 40
Answer: B. 16
Explanation: If you add a constant to each number at the data set, standard deviation doesn't change. However, multiplying each data in the data set by a constant, also multiplies the standard deviation by that constant.
That being said, the formulafor the adjusted test score is
y = 0.8x + 20
Adding 20 to each data doesn't change standard deviation but multiplying by 0.8 changes it.
So, the new standard deviation is
σ = 20*0.8 = 16
Standard Deviation for the adjusted test scores of the students is 16.