For below question I come up with the standard deviation of .9 but the answer key provide states .789 not sure where I am going wrong. I figured out the mean at 2.3.

(1-2.3)^2(.2)+(2-2.3)^2(.4)+(3-2.3)^2(.3)+(4-2.3)^2(.1)=.338+.036+.1470+.2890=.81

square root of .81 =.9

Does listening to soothing music help employees concentrate better?A psychologist studied the number of puzzles employees of a large business were able to solve in a five-minute period while listening to soothing music.Let X be the number of puzzles completed successfully by a randomly selected employee.The psychologist found that X had the following probability distribution:

Value of X1234

Probability0.20.40.30.1

The standard deviation of the number puzzles completed successfully is:

A) 1.0 B) 2.3 C) .789 D) .623