Live GMAT classes with Target Test Prep start Nov 21 and Nov 22. First class free.

See classes
Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

Newsweek Readers’ Choice Awards 2026 winner: Target Test Prep, #1 Test Prep

Target Test Prep was voted #1 Best Test Prep in the 2026 Newsweek Readers’ Choice™ Awards.

★★★★★5.0563 reviews
GMATLiveTeachStarts Nov 22
Josh Braslow, Target Test Prep GMAT expert
LIVE ONLINE CLASSES

Get Ready for GMAT Test Day Faster with Live Online Classes

with Josh Braslow, 20+ years in test prep

Nov 22 · Josh Braslow
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes + 6 months of TTP OnDemand
  • Attend the first class for free
  • Every class is recorded, so you never fall behind
View classes & enroll
Limited seats availableTarget Test Prep
EALiveTeachOnDemandStart anytime
EXECUTIVE ASSESSMENT

Target Test Prep EA OnDemand

Self-paced EA prep. Study on your schedule.

EXECUTIVE ASSESSMENT

with

165+ EA score guarantee
$05-day trial no automatic billing
Schedule
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll Start free 5-day trial
Limited cohort · enrollment openTrial includes full course accessTarget Test Prep
GMATOnDemandStart anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions

Different approaches to a problem

Expert replies
by jimmiejaz » Mon Nov 24, 2008 5:34 am
Hi guys,

I am stuck at this problem. I can figure this with the basic weighed avges but i want to know how to solve this problem if we take 100 and 200 gallons as 0 and 100 respectively and i am getting 35% instead of 30%.
Wat's the fault in my approach. please explain.

Mixture M consists of 65% water and 35% ethanol. Mixture N
consists of 80% water and 20% ethanol. If 200 gallons of
Mixture M is combined with 100 gallons of Mixture N, what
percent of the resulting solution is ethanol?

Approach one:
(.35*200+.2*100)/300 = 30%

Approach 2:
(.35*100+.2*0)/100 = 35%

why is the answer diff this time?
I am unable to figure out!!!!
What if i have not yet beat the beast, I know i will beat it!!!!!!!!
Join the discussion
Source: — Problem Solving |

by joanjgonzalez » Mon Nov 24, 2008 5:59 am
Hi Jimmiejaz,

I would say the correct approach is #1. In you 2nd approach you are mixing 100 gallons of M solution with no gallons (zero in your formula) of N mixture. Therefore, you obtain 35% solution. Note that this percentage corresponds to the percentage of the first solution and that that is obvious because you have mixed it with 0 liters of N (no N mixture).


Hope it is useful,

JJ
Join the discussion

jimmiejaz wrote:Hi guys,

I am stuck at this problem. I can figure this with the basic weighed avges but i want to know how to solve this problem if we take 100 and 200 gallons as 0 and 100 respectively and i am getting 35% instead of 30%.
Wat's the fault in my approach. please explain.

Mixture M consists of 65% water and 35% ethanol. Mixture N
consists of 80% water and 20% ethanol. If 200 gallons of
Mixture M is combined with 100 gallons of Mixture N, what
percent of the resulting solution is ethanol?

Approach one:
(.35*200+.2*100)/300 = 30%

Approach 2:
(.35*100+.2*0)/100 = 35%

why is the answer diff this time?
I am unable to figure out!!!!
If you change the ratio of the solution, of course you're going to get a different weighted average. The question clearly states how much of each mixture you're using, so I'm not sure why you'd want to change the numbers.

If you had kept the ratio the same, e.g. chosen 100M and 50N, you would have gotten the same result as the original. You changed a 2:1 ratio to a 1:0 ratio, something that violates the terms of the question.
Image

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course
Join the discussion

by jimmiejaz » Mon Dec 01, 2008 9:03 am
Thanks for the explanation stuart.

I was attempting this concept.
2 things cost 170 3 cost 180 wats the avg.
we can do it as
(2*0 + 3*10)/5 = 6
so avg is 176

How to apply it here?
OR Can i apply this approach on these type of questions?
What if i have not yet beat the beast, I know i will beat it!!!!!!!!
Join the discussion