Statistics linear transformation rescale

[bcahmel]

1. The problem statement, all variables and given/known data
Mean of 25 and standard deviation of 5. Rescale the test using linear transformation so that the mean is 100?
and the standard deviation is 20...



2. Relevant equations
xnew=a+bx


3. The attempt at a solution
I dont know...15+4x? I really dont understand how to calculate this. I read my book and its useless! Any help? :)
1. The problem statement, all variables and given/known data



2. Relevant equations



3. The attempt at a solution

[HallsofIvy]

Where did you get the "15"? 4(25)= 100 and 4(5)= 20. Looks to me like you just want to multiply by 4.

"I read my book and it is useless"
Then you can do nothing to improve the situation.

"I have trouble understanding my book"
Then you can work on reading the book more carefully and improve the situation.

Which do you prefer?

[bcahmel]

well the first one is true but I'd prefer the second one.