We need to divide 1½kg bags into 50kg: 50/(3/2)=2*50/3=100/3=33 full bags. 33*1½=33+16½=49½kg. So we can get 49½kg into 33 1½kg bags, but the remaining ½kg won't fill another bag. So the answer is 33 full bags.
We can put the remaining ½kg into another bag but it won't be full.