Stats question -quick help

Hi,

Does anyone know where to begin with this stats question- I know how to determine the mean/ standard deviation but I am not sure where to start and how to get the final standard d. value back into normal form from coded form:

Calculate mean + standard deviation of 20 observations of variable x using coding y= (x - 85) / 5

x: 75 80 85 90 95 100
F: 1 3 6 5 4 1

F = frequency.

Thanks.

Apply the code
Find the mean and sd
Dis-apply the code

I imagine that you have examples in your text book or notes

When you disapply the code, you would multiply the coded SD and then + 85 onto that value or the other way around?

This is where I am unsure, textbook isnt clear

Thanks for reply

The SD is only multiplied ... addition and subtractions have no impact on SD