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

percentage calculation

Expert replies
by lukaswelker » Thu Apr 17, 2014 8:12 am
Dear,

I'm almost able to resolve this one but I have a doubt with the result.

Here come the question,

At a certain factory, 10 percent of the staplers produced on Monday were defective and 2 percent of the non defective staplers were rejected by mistake. If 90 of the non defective staplers were rejected, what was the number of staplers produced that day?

4000 ; 4200 ; 4500 ; 4800 : 5000

At first I did the obvious mistake of considering that 90 staplers are equally to 2% of the researched amount.

After looking at it again, I realized my mistake and calculated the following.
90 represent (0.9*0.02 --> 0.018) 1.8% of the researched amount. This will imply that the final amount is closed to 5600. Which is a bit far of the 5000 given as the right answer.

Can anybody tell me if I'm doing something wrong? if yes, why :) ?

Many thanks
Lukas
Join the discussion
Source: — Problem Solving |

by theCodeToGMAT » Thu Apr 17, 2014 8:20 am
Produced = X
Defective = 0.1*x
Non-Defective = 0.9 * x
Rejected = 0.02 * 0.9 * x

90 = 0.02 * 0.9 * x

90 * 100 * 10 / 18 = x

x = 5000
R A H U L
Join the discussion

by GMATGuruNY » Thu Apr 17, 2014 5:23 pm
lukaswelker wrote:At a certain factory, 10 percent of the staplers produced on Monday were defective and 2 percent of the non defective staplers were rejected by mistake. If 90 of the non defective staplers were rejected, what was the number of staplers produced that day?

4000 ; 4200 ; 4500 ; 4800 : 5000
An alternate approach is the PLUG IN THE ANSWERS, which represent the total number of staplers.
2% of the middle answer choice -- 4500 -- is equal to 90.
But the problem states that 2% of ONLY THE NONDEFECTIVE STAPLERS = 90.
Thus, the total number of staplers must be GREATER than 4500.
Eliminate A, B and C.

Between D and E, E seems easier to evaluate.

E: 5000
Defective = 10% of 5000 = 500.
Nondefective = 5000-500 = 4500.
Rejected nondefective = 2% of 4500 = 90.
Success!

The correct answer is E.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Join the discussion

by ceilidh.erickson » Fri Apr 18, 2014 7:31 am
We can also solve this using an OVERLAPPING SETS matrix. (It's not strictly necessary in this problem, but it can be a helpful way of organizing information).
Image

Then, fill in the given information. Call the total number of staplers X, and infer that 10% defective means 90% not defective:

Image

Then, take 2% of the 90% that are not defective: 0.018x. We're told that that's equal to 90:

Image

Whenever we have two expressions in the same box of the matrix, we can set them equal:
0.018x = 90
(18/1000)x = 90
x = 5,000
90 represent (0.9*0.02 --> 0.018) 1.8% of the researched amount. This will imply that the final amount is closed to 5600. Which is a bit far of the 5000 given as the right answer.
You were right - 90 does represent 1.8% of the total. I'm not sure how you got your estimated amount of 5600. Often the easiest way to deal with percents when you don't have a calculator is by turning them into fractions.

Turn 0.018 into 18/1000, and when you cross-multiply, it will be easy to divide 90 by 18, then multiply by 1,000.

[/img]
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
Join the discussion

by Brent@GMATPrepNow » Fri Apr 18, 2014 9:06 am
Ceilidh's OVERLAPPING SETS matrix (aka "Double Matrix Method", aka "Group Grid") is a fast an easy way to organize information in overlapping sets questions. This technique can be used for most questions featuring a population in which each member has two characteristics associated with it.
Here, we have a population of staplers, and the two characteristics are:
- defective or not defective
- rejected or not rejected

To learn more about the Double Matrix Method, watch our free video: https://www.gmatprepnow.com/module/gmat- ... ems?id=919

Once you’re familiar with this technique, you can attempt these additional practice questions:

Easy Problem Solving questions
- https://www.beatthegmat.com/the-aam-aadm ... 72242.html
- https://www.beatthegmat.com/finance-majo ... 67425.html

Medium Problem Solving questions
- https://www.beatthegmat.com/probability- ... 73360.html
- https://www.beatthegmat.com/posted-speed ... 72374.html
- https://www.beatthegmat.com/motel-t271938.html
- https://www.beatthegmat.com/of-the-appli ... 70255.html
- https://www.beatthegmat.com/opening-nigh ... 64869.html
- https://www.beatthegmat.com/ds-french-ja ... 22297.html

Difficult Problem Solving questions
- https://www.beatthegmat.com/ratio-problem-t268339.html
- https://www.beatthegmat.com/overlapping- ... 65223.html
- https://www.beatthegmat.com/fractions-t264254.html
- https://www.beatthegmat.com/overlapping- ... 64092.html
- https://www.beatthegmat.com/mba/2011/05/ ... question-2

Easy Data Sufficiency questions
- https://www.beatthegmat.com/for-what-per ... 70596.html
- https://www.beatthegmat.com/ds-quest-t187706.html

Medium Data Sufficiency questions
- https://www.beatthegmat.com/sets-matrix-ds-t271914.html
- https://www.beatthegmat.com/each-of-peop ... 71375.html
- https://www.beatthegmat.com/a-manufacturer-t270331.html
- https://www.beatthegmat.com/in-costume-f ... 69355.html
- https://www.beatthegmat.com/mba/2011/05/ ... question-1

Difficult Data Sufficiency questions
- https://www.beatthegmat.com/double-set-m ... 71423.html
- https://www.beatthegmat.com/sets-t269449.html
- https://www.beatthegmat.com/mba/2011/05/ ... question-3

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Join the discussion