6 litres of pure acid is added to 10 l of a mixture of acid

Ravi 1596 wrote:6 litres of pure acid is added to 10 litres of a mixture of acid and water with 40% acid.What is the percentage of acid in the new solution

ORIGINAL mixture
Volume = 10 liters
40% acid
40% of 10 liters = 4 liters
So, the ORIGINAL mixture contains 4 liters of pure acid

NEW mixture
6 liters added to 10 liters = 16 liters
So, the TOTAL volume = 16 liters

The amount of pure acid in the NEW mixture = 4 liters + 6 liters = 10 liters

So, 10/16 of the NEW mixture is pure acid

10/16 = 5/8 = [spoiler]62.5%[/spoiler]

Cheers,
Brent

Hi Ravi 1596,

Both Brent and Mitch have explained the math behind this question, so I won't rehash any of that here. For future reference though, when posting GMAT questions, you should make sure to post the FULL question (with the 5 answer choices). Sometimes the answer choices are designed to give you a potential 'shortcut' (or help you to avoid a 'long' math approach), so as you continue to study, you should look to take advantage of ALL of the information that you're given to work with - and giving the other site members and Experts access to the full question can help us to show you all of those shortcuts.

GMAT assassins aren't born, they're made,
Rich

rsarashi wrote:Hello Experts,

What am I doing wrong?

10L mixture is given, so x be the acid in this mixture.

Now 6L of pure acid is added. So the equation would be like below.

(x+6/10+6)*100 = 40/100

Please explain if I understood the question in wrong way.

Thanks.

That calculation assumes that the NEW solution is 40% acid (AFTER the 6 liters of pure acid is added), whereas the question tells us that that ORIGINAL solution is 40% acid.

Ravi 1596 wrote:6 litres of pure acid is added to 10 l of a mixture of acid and water with 40% acid.What is the percentage of acid in the new solution

The current mixture contains 10 x 0.4 = 4 liters of acid and 6 liters of water. If 6 liters of acid are added, the amount of acid is now 10 liters and the total solution is now 16 liters.

Thus, the percentage of acid is 10/16 x 100 = 62.5%.