Some proportional problems may need ready recall of multiplications and and division but many can be explored with just addition and subtraction. Why leave it? Students love the reasoning challenges.
This is from The Wilkie Way Newsletter October 2015. Author Charlotte Wilkinson www.thewilkieway.co.nz
Try them with your students, and see how they get on. Dont tell them how to do them, let them explore and share their methods.