Answer:
Let there are 3 Containers.
Weight of Containers is w1,w2,w3 respectively.
Sand is filled in the containers one by one.
After filling the sand in three containers,
the weight of Containers become W1, W2, W3.
The difference between the weight of container after filling the sand and the actual weight of empty container, will give the weight of sand in that. Container
The difference between the weights (W1-w1) will give us the weight of sand in first container.
The difference between the weights (W2-w2) will give us the weight of sand in Second container.
The difference between the weights (W3-w3) will give us the weight of sand in Third container.
Explanation: