Question

A shop keeper used only 4 weights to weigh any article between 1 kg and 40 kgs.what r the weights

Answer 1

it may be 1 kg, 3 kg, 9 kg, 27 kg

so for example you want to weigh  2 kg apples

but you have only 1 and 3 kg

so you put 2 kg apples in one side and put 3kg weight in other side

now you see that the weight is heavier so now up put 1 kg weight in apple side therefore you see its balanced

or now you want 40 kg

you just use all the weights!