BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

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.

★★★★★5.0559 reviews
GMATLiveTeach 7 seats left
Chris Peckover
NEXT LIVE COHORT

Oct 13 to Jan 7, 2027

with Chris Peckover

Schedule
Tue, Thu · 8:00 to 10:00 PM ET
Included
40 live hours + 6 months of GMAT OnDemand
  • Live instruction and real-time questions
  • Class recordings and assigned practice
View class & enroll
Limited cohort · enrollment openTarget Test Prep
EALiveTeach 5 seats left
Logan Thompson
EXECUTIVE ASSESSMENT

Sep 6 to Dec 6, 2026

with Logan Thompson

Schedule
Sun · 9:30 AM to 12:30 PM ET
Included
Live EA class + 6 months of EA OnDemand
  • Expert-led weekly online sessions
  • EA Masterclass access between classes
View EA class & enroll
Limited cohort · enrollment openTarget Test Prep
GMATOnDemand Start anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

130-point score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 559 reviewsTarget Test Prep

Compare the format, schedule, and included access before enrolling. Prices and seat counts shown reflect the supplied offer details.

The product (1−1/2)(1−1/3)(1−1/4)(1−1/5)...

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Moderator
Posts: 2575
Joined: Sun Oct 15, 2017 1:50 pmFollowed by: 6 members
by BTGmoderatorLU » Sat Oct 21, 2017 6:57 pm
The product
$$\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right)\left(1-\frac{1}{4}\right)\left(1-\frac{1}{5}\right).........\left(1-\frac{1}{19}\right)\left(1-\frac{1}{20}\right)$$
equals...

$$A:\frac{1}{10}$$

$$B:\frac{1}{20}$$

$$C:\frac{3}{20}$$

$$D:\frac{3}{10}$$

$$E:\frac{7}{20}$$

The OA is B.

Can any expert help me with this PS question please? Thanks.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members
Location: New York, NY
Thanked: 13060 times
GMAT Score:790

by GMATGuruNY » Sun Oct 22, 2017 3:57 am
LUANDATO wrote:The product
$$\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right)\left(1-\frac{1}{4}\right)\left(1-\frac{1}{5}\right).........\left(1-\frac{1}{19}\right)\left(1-\frac{1}{20}\right)$$
equals...

$$A:\frac{1}{10}$$

$$B:\frac{1}{20}$$

$$C:\frac{3}{20}$$

$$D:\frac{3}{10}$$

$$E:\frac{7}{20}$$
In the solution below, all of the values in red CANCEL OUT.

$$\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right)\left(1-\frac{1}{4}\right)\left(1-\frac{1}{5}\right).........\left(1-\frac{1}{19}\right)\left(1-\frac{1}{20}\right)$$

= (1/2)(2/3)(3/4)....(17/18)(18/19)(19/20).

= 1/20.

The correct answer is B.
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
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 8177
Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members
Location: Los Angeles, CA
Thanked: 43 times

by Scott@TargetTestPrep » Wed Nov 20, 2019 6:02 pm
BTGmoderatorLU wrote:The product
$$\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right)\left(1-\frac{1}{4}\right)\left(1-\frac{1}{5}\right).........\left(1-\frac{1}{19}\right)\left(1-\frac{1}{20}\right)$$
equals...

$$A:\frac{1}{10}$$

$$B:\frac{1}{20}$$

$$C:\frac{3}{20}$$

$$D:\frac{3}{10}$$

$$E:\frac{7}{20}$$

The OA is B.

Can any expert help me with this PS question please? Thanks.

Solving the product for the 1st four parentheses, we have:

(1/2) x (2/3) x (3/4) x (4/5) x ... x (18/19) x (19/20)

After cross canceling, we see that only the numerator of the first fraction and the denominator of the last fraction remain. Thus, the product of the entire expression is 1/20.

Answer: B

Scott Woodbury-Stewart
Founder and CEO
[email protected]

Image

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

ImageImage
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1