A chemical supply company has 60 liters of a 40% HNO3 solution.

Question

A chemical supply company has 60 liters of a 40% HNO3 solution. How many liters of pure undiluted HNO3 must the chemists add so that the resultant solution is a 50% solution?

A) 12
B) 15
C) 20
D) 24
E) 30

abhimahna · Accepted Answer

Another simple one.

60 liters of a 40% HNO3 solution means HNO3 = 24 liters in 60 liters of the solution.

Now, let x be the pure HNO3 added.

As per question,

24 + x = 50% of (60 + x)

or x =12. Hence, A

colorblind · Answer

Use weighted Avg:

\frac{W1}{W2}=\frac{(A2-Avg)}{(Avg-A1)} 
Here W1 = 60; W2 is what we need to find.
Avg = 50%; A1 = 40%; A2 = 100%
 \frac{60}{W2}=\frac{(100-50)}{(50-40)}=\frac{5}{1} 
W2 = 12

JeffTargetTestPrep · Answer

We can lert n = the amount of pure undiluted HNO3 to be added and create the equation:

(0.4 x 60 + n)/(60 + n) = 1/2

2(24 + n) = 60 + n

48 + 2n = 60 + n

n = 12

Answer: A

EMPOWERgmatRichC · Answer

Hi swerve,

We're told that a chemical supply company has 60 liters of a 40% HNO3 solution. We're asked for the number of liters of pure undiluted (meaning 100%) HNO3 the chemists must add so that the resultant solution is a 50% solution. This question is essentially a 'Weighted Average' question, but there's a math 'shortcut' that you can use to simplify the calculations involved. We can TEST THE ANSWERS to take advantage of the shortcut.

To start, since we're mixing in a pure (100%) solution, it won't take much of that solution - relatively speaking - to raise a 40% solution to an overall 50% solution. Thus, the correct answer is likely one of the smaller answers. Both Answer A (12) and Answer B (15) are factors of 60, so those numbers would form a simple ratio (1:5 and 1:4, respectively) with the 60 liters that are already there. This means that we can calculate the average using the ratio - and not the larger numbers involved.

Answer A: 12 liters --> forms a ratio of 1:5 with the original 60 liter mixture

/(1+5) = 300%/6 = 50% 
This is an exact match for what we were told, so this must be the answer

Final Answer:  A

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

fskilnik · Answer

Perfect opportunity for the  Alligation  and  Bruce Lee  (when we make numerators equal)!

https://preview.ibb.co/mPxqs0/13-Nov18-4w.gif

? = x

\frac{{60}}{{60 + x}} = \frac{{100 - 50}}{{100 - 40}} = \frac{{5 \cdot \boxed{12}}}{{6 \cdot \boxed{12}}}\,\,\,\,\,\,\,\, \Rightarrow \,\,\,\,\,60 + x = 72\,\,\,\,\,\,\,\,\,\,\, \Rightarrow \,\,\,\,? = x = 12

This solution follows the notations and rationale taught in the GMATH method.

Regards, 
Fabio.

CLIMBTHELADDER · Answer

Does anyone have a log of questions similar to this one? Please relay!

Bunuel

jfranciscocuencag · Answer

Hello!

Could someone please explain to me why I can't solve it by the attached image?

Thank you so much!

bumpbot · Answer

Automated notice from GMAT Club BumpBot:

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

This post was generated automatically.

A chemical supply company has 60 liters of a 40% HNO3 solution.

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Problem Solving (PS) Questions

A chemical supply company has 60 liters of a 40% HNO3 solution.

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards