A packet sold at a 10% loss had a price of $9, thus the cost of a packet is $10.

50 packets was sold at a 5% profit --> gives profit of 10*0.05*50 = $25.
50 packets was sold at a 10% loss --> gives loss of 10*0.1*50 = $50.

The overall loss is $25 - $50 = $25.

Answer: C.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Hi iNumbv,

The math involved in this question can be done in a variety of ways; it's just a matter of what method you find most comfortable.

Here, we're told that a person bought 150 packets of chocolate...

We can say that 1 packet cost $X

We then sell 50 each at....
a 5% profit = 1.05X each
a 0% profit = 1X each
a 10% loss = .9X each

Since the question focuses on the net profit or loss, we can ignore the 50 packets we sold for a 0% profit and focus on the other 100.

50(1.05X + .9X) =
50(1.95X)

IF we had 50(2X), then we would have 0 profit.
Here we have 50(1.95X), so we clearly lost money.

The .05X that we lost can be quantified as 50(.05X) = 2.5X
Once we know the purchase price (X) of each packet, then we can just plug in and we'll know the total loss.

We're told that the price of a "10% loss" packet = $9, so the original price = $10. We can plug that in for X...

2.5(10) = 25 dollars lost

Final Answer:

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

760+: Learn What GMAT Assassins Do to Score at the Highest Levels
Contact Rich at: Rich.C@empowergmat.com

***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources