16/5 = 3 ... 1, so 5 kg can't hold more than 3 bags.

Starting with a bag, if a bag weighs 5 kg, there is still 1 1 kg left, and 2 kg cannot be divided equally.

If there are two bags of 5 kilograms, there are still 6 kilograms left, which is exactly 3 bags of 2 kilograms.