math
posted by Helen .
Each element in a data set is multiplied by 2, and each resulting product is then increased by 5. If 'm' is the mean of the final data set, which of the following expressions gives the mean of the original set in terms of 'm'?
~why is the answer (1/2)(m5)?

the transformation is :
multiply by 2, then add 5
to get back to where we started from, we have to not only do the inverse of each operation but also reverse the order in which these operations were done.
the last thing we did was add 5, so the first thing we have to do in the inverse is to subtract 5, thus the (m5)
the first thing we did was multiply by 2, so the last thing we do in the inverse is divide by 2, thus the (m5)/2
or
(1/2)(m5) 
thank you