How many number of weights do you need to weight 31 kg of Rice if you have one kg of weight stone ?

There are total 5 ways.
we have only one kg of weight so,
2kg = 1kg + 1kg
4kg = 1 + 2 + 1
8kg = 1 + 2 + 4 + 1
16kg = 1 + 2 + 4 + 8 + 1
31kg = 1 + 2 + 4 + 8 + 16
So 5 weights are needed.