Functions

Expert replies

BTGmoderatorRO: Moderator; Posts: 772; Joined: Wed Aug 30, 2017 6:29 pmFollowed by: 6 members

by BTGmoderatorRO » Sat Oct 28, 2017 2:31 am

Let function f(x)=(x-a)(x-b). If f(10)=f(20)=0, f(30)=?

A. 50
B. 100
C. 150
D. 200
E. 250
OA is d
what approach can we use to get the correct answer?

Like this post

Source: Beat The GMAT — Problem Solving | Sat Oct 28, 2017 2:31 am

GMATGuruNY: 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 » Sat Oct 28, 2017 3:06 am

Roland2rule wrote:Let function f(x)=(x-a)(x-b). If f(10)=f(20)=0, f(30)=?

A. 50
B. 100
C. 150
D. 200
E. 250

f(10) = 0 implies (10, 0) is a point on the graph of f(x)=(x-a)(x-b).
Implication:
f(x) = (x-10)(x-b), with the result that x=10 yields f(x)=0.

f(20) = 0 implies (20, 0) is a point on the graph of f(x)=(x-10)(x-b).
Implication:
f(x) = (x-10)(x-20), with the result that x=20 yields f(x)=0.

Substituting x=30 into f(x) = (x-10)(x-20), we get:
f(x) = (30-10)(30-20) = (20)(10) = 200.

The correct answer is D.

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

Like this post

GMAT/MBA Expert

Scott@TargetTestPrep: GMAT Instructor; Posts: 8138; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

by Scott@TargetTestPrep » Tue Nov 12, 2019 7:20 pm

BTGmoderatorRO wrote:Let function f(x)=(x-a)(x-b). If f(10)=f(20)=0, f(30)=?

A. 50
B. 100
C. 150
D. 200
E. 250
OA is d
what approach can we use to get the correct answer?

Since f(10) = f(20) = 0, this means a = 10 and b = 20, or vice versa. In other words, f(x) = (x - 10)(x - 20). Therefore, f(30) = (30 - 10)(30 - 20) = (20)(10) = 200.

Answer: D

Scott Woodbury-Stewart
Founder and CEO
[email protected]

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

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review