Enough salt was added to 30kilos of a 10% salt solution to increase the salt concentration to 25%. How many kilos of salt were added?
Ans:
Originally the solution is 30 Kg an has 10% salt. i.e. the weight of salt
in the solution = 30*10% = 3 Kg.
Let us say we added x kg of salt.
Now in the new solution, weight of salt = 3 + x
Weight of the new solution = 30 + x
If this is a 25% solution, it means that

or


 or 

So, 6 kg of salt were added to make it 25% concentration.

Hope you got it:)