Samantha has five objects weighing 1kg,2kg,3kg,4kg and 5kg. If she weighs them two at a time, how many different weighs can she get?

Answer 1

There are 5C2 = 10 ways to select the weights. However, there are some duplicates, such as

1+5 and 2+4

I suppose you can find how many, and subtract them from 10.