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

 It is currently 20 Oct 2019, 22:04

### 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: 56
Power saving of a bulb is directly proportional to square root  [#permalink]

### Show Tags

04 Sep 2016, 10:41
1
3
00:00

Difficulty:

45% (medium)

Question Stats:

60% (01:59) correct 40% (02:17) wrong based on 97 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: 3578
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.
New! Best Reply Functionality on GMAT Club!
Find a bug in the new email templates and get rewarded with 2 weeks of GMATClub Tests for free
Check our new About Us Page here.
Director
Joined: 27 May 2012
Posts: 906
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: 3578
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.
New! Best Reply Functionality on GMAT Club!
Find a bug in the new email templates and get rewarded with 2 weeks of GMATClub Tests for free
Check our new About Us Page here.
Director
Joined: 27 May 2012
Posts: 906
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
Non-Human User
Joined: 09 Sep 2013
Posts: 13321
Re: Power saving of a bulb is directly proportional to square root  [#permalink]

### Show Tags

20 Jan 2019, 02:26
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Re: Power saving of a bulb is directly proportional to square root   [#permalink] 20 Jan 2019, 02:26
Display posts from previous: Sort by