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

 It is currently 21 Jul 2018, 12:38

### 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

# Power saving of a bulb is directly proportional to square root

Author Message
TAGS:

### Hide Tags

Manager
Joined: 15 Apr 2016
Posts: 82
Power saving of a bulb is directly proportional to square root  [#permalink]

### Show Tags

04 Sep 2016, 10:41
1
00:00

Difficulty:

45% (medium)

Question Stats:

57% (01:14) correct 43% (01:54) wrong based on 65 sessions

### HideShow timer Statistics

Power saving (in %) of a bulb is directly proportional to square root of its efficiency. By how much % is power saving of bulb-1(efficiency 0.8) greater than power saving of bulb-2 (efficiency 0.2)?

A. 60%
B. 70%
C. 80%
D. 90%
E. 100%

_________________

Cheers,
Shri
-------------------------------
GMAT is not an Exam... it is a war .. Let's Conquer !!!

Board of Directors
Status: Stepping into my 10 years long dream
Joined: 18 Jul 2015
Posts: 3687
Re: Power saving of a bulb is directly proportional to square root  [#permalink]

### Show Tags

04 Sep 2016, 11:11
Shrivathsan wrote:
Power saving (in %) of a bulb is directly proportional to square root of its efficiency. By how much % is power saving of bulb-1(efficiency 0.8) greater than power saving of bulb-2 (efficiency 0.2)?

A. 60%
B. 70%
C. 80%
D. 90%
E. 100%

Power, $$P1 = k * sqrt(0.8)$$

Power, $$P2 = k * sqrt(0.2)$$

Difference = $$P1-P2 = k * sqrt(0.8) - k * sqrt(0.2)$$

% greater =$$k * sqrt(0.8) - k * sqrt(0.2)/k * sqrt(0.2) * 100$$

= 100%.

Hence, E
_________________

My GMAT Story: From V21 to V40
My MBA Journey: My 10 years long MBA Dream
My Secret Hacks: Best way to use GMATClub | Importance of an Error Log!
Verbal Resources: All SC Resources at one place | All CR Resources at one place

GMAT Club Inbuilt Error Log Functionality - View More.
New Visa Forum - Ask all your Visa Related Questions - here.

Find a bug in the new email templates and get rewarded with 2 weeks of GMATClub Tests for free

Director
Joined: 27 May 2012
Posts: 513
Power saving of a bulb is directly proportional to square root  [#permalink]

### Show Tags

13 Nov 2017, 10:53
abhimahna wrote:
Shrivathsan wrote:
Power saving (in %) of a bulb is directly proportional to square root of its efficiency. By how much % is power saving of bulb-1(efficiency 0.8) greater than power saving of bulb-2 (efficiency 0.2)?

A. 60%
B. 70%
C. 80%
D. 90%
E. 100%

Power, $$P1 = k * sqrt(0.8)$$

Power, $$P2 = k * sqrt(0.2)$$

Difference = $$P1-P2 = k * sqrt(0.8) - k * sqrt(0.2)$$

% greater =$$k * sqrt(0.8) - k * sqrt(0.2)/k * sqrt(0.2) * 100$$

= 100%.

Hence, E

Can you please elaborate how to simply this.

Quote:
% greater =$$k * sqrt(0.8) - k * sqrt(0.2)/k * sqrt(0.2) * 100$$

_________________

- Stne

Board of Directors
Status: Stepping into my 10 years long dream
Joined: 18 Jul 2015
Posts: 3687
Power saving of a bulb is directly proportional to square root  [#permalink]

### Show Tags

13 Nov 2017, 11:03
1
stne wrote:
Can you please elaborate how to simply this.

Quote:
% greater =$$k * sqrt(0.8) - k * sqrt(0.2)/k * sqrt(0.2) * 100$$

Here I go:

$$sqrt(0.8)$$ = sqrt(8)/sqrt(10) = [2*sqrt(2)]/sqrt(10)

$$sqrt(0.2)$$ = sqrt(2)/sqrt(10)

You know we can cancel 'k' from denominator and numerator.

Similarly, you have sqrt(10) both at numerator and denominator, so you can cancel that out.

Therefore, you are left with [2*sqrt(2) - sqrt(2) ] / sqrt(2) ] *100 = [sqrt(2) ] / sqrt(2)] *100 = 100%

Does that make sense?
_________________

My GMAT Story: From V21 to V40
My MBA Journey: My 10 years long MBA Dream
My Secret Hacks: Best way to use GMATClub | Importance of an Error Log!
Verbal Resources: All SC Resources at one place | All CR Resources at one place

GMAT Club Inbuilt Error Log Functionality - View More.
New Visa Forum - Ask all your Visa Related Questions - here.

Find a bug in the new email templates and get rewarded with 2 weeks of GMATClub Tests for free

Director
Joined: 27 May 2012
Posts: 513
Re: Power saving of a bulb is directly proportional to square root  [#permalink]

### Show Tags

13 Nov 2017, 11:15
abhimahna wrote:
stne wrote:
Can you please elaborate how to simply this.

Quote:
% greater =$$k * sqrt(0.8) - k * sqrt(0.2)/k * sqrt(0.2) * 100$$

Here I go:

$$sqrt(0.8)$$ = sqrt(8)/sqrt(10) = [2*sqrt(2)]/sqrt(10)

$$sqrt(0.2)$$ = sqrt(2)/sqrt(10)

You know we can cancel 'k' from denominator and numerator.

Similarly, you have sqrt(10) both at numerator and denominator, so you can cancel that out.

Therefore, you are left with [2*sqrt(2) - sqrt(2) ] / sqrt(2) ] *100 = [sqrt(2) ] / sqrt(2)] *100 = 100%

Does that make sense?

Took a while to realize this but finally got it. Yes it makes perfect sense.
Thanks a ton +1
_________________

- Stne

Re: Power saving of a bulb is directly proportional to square root &nbs [#permalink] 13 Nov 2017, 11:15
Display posts from previous: Sort by

# Events & Promotions

 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®.