GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 18 Apr 2019, 08:18

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

If the operation ∆ is defined by a∆b = (b-a)^2/a^2 for all number a

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:

Hide Tags

Intern
Joined: 26 May 2015
Posts: 7
If the operation ∆ is defined by a∆b = (b-a)^2/a^2 for all number a  [#permalink]

Show Tags

17 Jul 2017, 12:57
00:00

Difficulty:

15% (low)

Question Stats:

81% (01:08) correct 19% (01:27) wrong based on 50 sessions

HideShow timer Statistics

If the operation ∆ is defined by a∆b = (b-a)^2/a^2 for all number a and b, and a ≠ 0, then -1∆(1∆ -1) =

a. -1
b. 0
c. 1
d. 9
e. 25
Senior Manager
Joined: 24 Apr 2016
Posts: 331
Re: If the operation ∆ is defined by a∆b = (b-a)^2/a^2 for all number a  [#permalink]

Show Tags

17 Jul 2017, 15:20
1
-1∆(1∆ -1) = -1∆[(-1-1)^2]/1 = -1∆4 = [(4+1)^2]/1 = 25
Senior SC Moderator
Joined: 22 May 2016
Posts: 2632
Re: If the operation ∆ is defined by a∆b = (b-a)^2/a^2 for all number a  [#permalink]

Show Tags

17 Jul 2017, 18:55
1
Esguitar wrote:
If the operation ∆ is defined by a∆b = $$(b-a)^2/a^2$$ for all number a and b, and a ≠ 0, then -1∆(1∆ -1) =
a. -1
b. 0
c. 1
d. 9
e. 25

Or, the longish way (not too bad - 54 seconds)

If a∆b = $$\frac{(b-a)^2}{a^2}$$, then

-1∆(1∆ -1) =

1. Parentheses first:

(1∆ -1) = $$\frac{(-1-1)^2}{(1)^2}$$ = $$\frac{(-2)^2}{1}$$ = $$\frac{4}{1}$$ = 4

4 becomes b -->

2. New expression is -1 ∆ 4

$$\frac{(4-(-1))^2}{(-1)^2}$$ = $$\frac{(5)^2}{1}$$ = $$\frac{25}{1}$$ = 25

Answer E
_________________
Listen, are you breathing just a little, and calling it a life?
-- Mary Oliver

For practice SC questions with official explanations that were posted and moderated by the SC Team,
go to SC Butler here: https://gmatclub.com/forum/project-sc-butler-get-2-sc-questions-everyday-281043.html
Intern
Joined: 26 May 2015
Posts: 7
Re: If the operation ∆ is defined by a∆b = (b-a)^2/a^2 for all number a  [#permalink]

Show Tags

18 Jul 2017, 02:13
Thanks a lot, I got it.
I could not see how the expression (1∆ -1) becomes (−1−1)^2/(1)^2, I assume that it is plugin number where a=1 and b=-1.
Thanks again.
Re: If the operation ∆ is defined by a∆b = (b-a)^2/a^2 for all number a   [#permalink] 18 Jul 2017, 02:13
Display posts from previous: Sort by

If the operation ∆ is defined by a∆b = (b-a)^2/a^2 for all number a

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.