Bunuel wrote:

What percent of the solution is water?

(1) Adding 5 liters of water increases the percentage of water by 20%.

(2) There are 30 liters of solution before any additions or subtractions from the solution.

Let P litres be the quantity of Initial solution, containing x litres of water.

hence % of water in Initial solution = \({(x/P) * 100}\)

Statement 1 says Adding 5 litres of water increases the % of water by 20%

Therefore New Quantity of Solution = (P+5) litres, containing (x+5) litres of water.

% Increase = \({(x+5)/(P+5)} - {(x/P)} = 20/100\)

we get an equation in 2 unknowns, hence St 1 alone is Insufficient.

Statement 2 says Quantity of Initial Solution, P = 30 litres, since no other info is provided, we can safely say St 2 alone is Insufficient.

Combining St 1 & 2

We can solve the equation in St 1, by substituting P = 30 & find value of x.

St 1 & 2 together are Sufficient.

Answer C.

Thanks,

GyM