GMAT Question of the Day: Daily via email | Daily via Instagram New to GMAT Club? Watch this Video

 It is currently 02 Jun 2020, 10:16

### 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

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

# Which of the following is the closest to 11*1020–9*1010?

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

### Hide Tags

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 9018
GMAT 1: 760 Q51 V42
GPA: 3.82
Which of the following is the closest to 11*1020–9*1010?  [#permalink]

### Show Tags

23 Aug 2017, 00:24
00:00

Difficulty:

35% (medium)

Question Stats:

63% (01:24) correct 37% (01:29) wrong based on 151 sessions

### HideShow timer Statistics

Which of the following is the closest to $$11*10^{20}–9*10^{10}$$?

A. $$10^2$$
B. $$10^7$$
C. $$10^{10}$$
D. $$10^{20}$$
E. $$10^{21}$$

_________________
MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $79 for 1 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Director Joined: 04 Dec 2015 Posts: 725 Location: India Concentration: Technology, Strategy WE: Information Technology (Consulting) Which of the following is the closest to 11*1020–9*1010? [#permalink] ### Show Tags 23 Aug 2017, 01:34 1 MathRevolution wrote: Which of the following is the closest to $$11*10^{20}–9*10^{10}$$? A. $$10^2$$ B. $$10^7$$ C. $$10^{10}$$ D. $$10^{20}$$ E. $$10^{21}$$ $$11*10^{20}–9*10^{10}$$ We can use approximate value. Hence we can use $$10$$ in place of $$11$$ and $$10$$ in place of $$9$$. $$(10*10^{20}) – (10*10^{10})$$ $$10^{(20+1)}–10^{(10+1)}$$ $$10^{21}–10^{11}$$ $$10^{11}(10^{10}–1)$$ $$1$$ is very small value compared to $$10^{10}$$. Hence $$1$$ can be ignored. Therefore $$(10^{10}–1) =$$ approximately $$= 10^{10}$$ $$(10^{11})(10^{10})$$ $$10^{(11+10)}$$ $$= 10^{21}$$ Answer (E)... _________________ Please Press "+1 Kudos" to appreciate. Senior PS Moderator Joined: 26 Feb 2016 Posts: 3253 Location: India GPA: 3.12 Which of the following is the closest to 11*1020–9*1010? [#permalink] ### Show Tags 23 Aug 2017, 04:39 We have been asked to find the value of the expression $$11*10^{20}–9*10^{10}$$ $$11*10^{20}–9*10^{10}$$ = $$11*10^{10}*10^{10} – 9*10^{10}$$ = $$10^{10}(11*10^{10} – 9)$$ Since we need an approximate value and the overall expression has extremely large numbers, we can assume both 11 and 9 to be equal to 10 The expression now becomes $$10^{10}(10*10^{10} – 10) = 10^{10}*10^1(10^{10} – 1) = 10^{10+1}(10^{10} – 1)$$ = $$10^{11}(10^{10})$$ Since a difference of 1 does not influence the value of the expression to that extent, the value must be $$10^{21}$$ approximately (Option E) _________________ You've got what it takes, but it will take everything you've got Manager Joined: 27 Dec 2016 Posts: 218 Concentration: Marketing, Social Entrepreneurship GPA: 3.65 WE: Marketing (Education) Which of the following is the closest to 11*1020–9*1010? [#permalink] ### Show Tags 23 Aug 2017, 18:26 MathRevolution wrote: Which of the following is the closest to $$11*10^{20}–9*10^{10}$$? A. $$10^2$$ B. $$10^7$$ C. $$10^{10}$$ D. $$10^{20}$$ E. $$10^{21}$$ 1. Factoring $$10^{10}$$ out = $$10^{10} (11*10^{10} - 9)$$ 2. Since we are asked about approximation, so we can use our estimation. 3. 11 and 10 is closest to 10, so I can change them to 10 --> $$10^{10} (10^1*10^{10} - 10^1)$$ --> $$10^{10} (10^{11} - 10^1)$$ 4. Difference between $$10^{11}$$ and $$10^{10}$$ is so HUGE, so can we can IGNORED this subtraction by $$10^1$$. 5. Therefore, $$10^{10} * 10^{11} = 10^{21}$$. E. _________________ There's an app for that - Steve Jobs. Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 9018 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Which of the following is the closest to 11*1020–9*1010? [#permalink] ### Show Tags 25 Aug 2017, 00:13 => $$9*10^{10}$$ is a relatively small number compared with $$11*10^{20}$$. $$11*10^{20}–9*10^{10}$$ is approximate to $$11*10^{20}$$, which is similar to $$10^{21}$$. Ans: E _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$79 for 1 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"
Manager
Joined: 30 Dec 2016
Posts: 224
GMAT 1: 650 Q42 V37
GPA: 4
WE: Business Development (Other)
Re: Which of the following is the closest to 11*1020–9*1010?  [#permalink]

### Show Tags

28 Aug 2017, 08:01
1
i did it this way.

Factor out 10^20 .

10^20 ( 11 - 9 * 10^-10 )
Now,
10^20 ( 11 - 0.000000009) we know from here that ( 11 - 0.000000009 ) will be 10.something .

So,
10^20 * 10.something = 10^21 .

Regards

SandySilva
Manager
Joined: 02 Nov 2015
Posts: 160
GMAT 1: 640 Q49 V29
Re: Which of the following is the closest to 11*1020–9*1010?  [#permalink]

### Show Tags

28 Aug 2017, 08:04
1
sandysilva wrote:
i did it this way.

Factor out 10^20 .

10^20 ( 11 - 9 * 10^-10 )
Now,
10^20 ( 11 - 0.000000009) we know from here that ( 11 - 0.000000009 ) will be 10.something .

So,
10^20 * 10.something = 10^21 .

Regards

SandySilva

Great one !!!!

Sent from my Lenovo TAB S8-50LC using GMAT Club Forum mobile app
Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 10644
Location: United States (CA)
Re: Which of the following is the closest to 11*1020–9*1010?  [#permalink]

### Show Tags

29 Aug 2017, 16:21
MathRevolution wrote:
Which of the following is the closest to $$11*10^{20}–9*10^{10}$$?

A. $$10^2$$
B. $$10^7$$
C. $$10^{10}$$
D. $$10^{20}$$
E. $$10^{21}$$

Since 9 x 10^10 is much smaller than 11 x 10^20, magnitude-wise, subtracting it from 11 x 10^20 would still be about 11 x 10^20. Since 11 is close to 10, 11 x 10^20 is approximately 10 x 10^20, magnitude-wise, and we have:

10 x 10^20 = 10^21

_________________

# Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com
202 Reviews

5-star rated online GMAT quant
self study course

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

Re: Which of the following is the closest to 11*1020–9*1010?   [#permalink] 29 Aug 2017, 16:21

# Which of the following is the closest to 11*1020–9*1010?

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

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne