Resizing

[jibber11]

I have a quick question.... Why if I have a photo cropped to 8 x 10 in PS, and if I resize the print to a 5x7 for printing, why does it not let me go to 5x7 without resizing to some odd size? exp. 7x5.6 or 5x6.25? Oh and I do have constrain proportions checked. if I uncheck it it seems to distort the image. Just came here for a quick answer instead of digging through all kinds of books! Thanks as always for all the help! This site is the best one I ever came across for photography!!!