Awater pitcher weighs 1.72 kg when empty and 2.01 kg when filled with water. how much does the water weigh?

So the beginning weight is 1.72 kg, but the end result is 2.01 kg.

So you are trying to find what #(number) plus 1.72 equals 2.01

This can also be written as 
You're trying to solve for x.

But since this problem is really simple, you just subtract 1.72 from 2.01
So, 2.01 - 1.72 

Which equals to 0.29kg of water :)

If you have any questions, let me know :)

Google it that might work