Hello, agus hendro!
Here's the first one . . .
Consider the number of kgs of water at each stage.1. 1000 kgs of chemical is stored in a container.
The chemical is made up of 99% water and 1% oil.
Some water is evaporated until the water content is reduced to 96%.
How much does the chemical weigh now?
We start with 1000 kgs of solution which is 99% water.
. . It contains: . kgs of water.
We remove kgs of water.
. . It now contains: . kgs of water.
Start again . . . We have 1000 kgs of solution.
. . We remove kgs of water.
So we have: kgs of stuff.
But this is supposed to be 96% water.
. . So it contains: . kgs of water.
We just described the final amount of water in two ways.
There is our equation! . . . .