circular gears

Forum Index GMAT Math Problem Solving

New MBA Student Life Forum: Ask your questions to current MBA students from Harvard, Stanford, Wharton, Kellogg and Haas

Post new topic   Reply to topic

LevelOne
Rising GMAT Star



Joined: 19 Jun 2009
Posts: 69

Thanks given: 10
Thanked 1 times in 1 posts
Location: London

Test Date: 13 June 2009
Target GMAT Score: 700+
Topic: circular gears
PostFri Jul 03, 2009 1:06 pm Reply with quote
1) Circular gears P and Q start rotating at the same time at constant speeds. Gear P makes 10 revolutions per minute, and gear Q makes 40 revolutions per minute. How many seconds after the gears start rotating will gear Q have made exactly 6 more revolutions than gear P?

A. 6
B. 8
C. 10
D. 12
E. 15

2) The value of 10^8 - 10^2/10^7 - 10^3 is closest to which of the following?

A. 1
B. 10
C. 10^2
D. 10^3
E. 10^4

thanks
Back to top
View user's profile Send private message
mehravikas
GMAT Destroyer!



Joined: 12 May 2008
Posts: 920

Thanks given: 23
Thanked 13 times in 13 posts
Location: Sydney

Test Date: ********
Target GMAT Score: 740
PostFri Jul 03, 2009 8:21 pm Reply with quote
Answer to Question 1 -

P = 10 rev per minute -> in one second it makes 10/60 = 1/6 rev per sec
Q = 40 rev per min -> in 1 sec = 40/60 = 2/3 rev per sec

1/6 * t + 6 = 2/3 * t

solve for t and you'll get 12. Answer D
Back to top
View user's profile Send private message Send e-mail
LevelOne
Rising GMAT Star



Joined: 19 Jun 2009
Posts: 69

Thanks given: 10
Thanked 1 times in 1 posts
Location: London

Test Date: 13 June 2009
Target GMAT Score: 700+
PostFri Jul 03, 2009 10:37 pm Reply with quote
OA is D. how about exponents in (2)?
Back to top
View user's profile Send private message
rahulg83
GMAT Destroyer!



Joined: 04 Nov 2008
Posts: 548

Thanks given: 26
Thanked 13 times in 12 posts
Location: India

Test Date: 09-Jul-2009
GMAT Score: 710
PostSat Jul 04, 2009 5:19 am Reply with quote
Quote:
2) The value of 10^8 - 10^2/10^7 - 10^3 is closest to which of the following?

A. 1
B. 10
C. 10^2
D. 10^3
E. 10^4
i suppose question asks for value of (10^8 - 10^2)/(10^7 - 10^3), it can be written as 10^2{(10^6)-1}/10^3{(10^4)-1}, now 1 can be neglected in comparison with 10^6 or 10^4

So our expression will now reduce to (10^2*10^6)/(10^3*10^4)=10 ans..
_________________
You know what you want...keep moving towards it
Back to top
View user's profile Send private message
LevelOne
Rising GMAT Star



Joined: 19 Jun 2009
Posts: 69

Thanks given: 10
Thanked 1 times in 1 posts
Location: London

Test Date: 13 June 2009
Target GMAT Score: 700+
PostSat Jul 04, 2009 5:31 am Reply with quote
rahulg83, thanks again.
Back to top
View user's profile Send private message
mehravikas
GMAT Destroyer!



Joined: 12 May 2008
Posts: 920

Thanks given: 23
Thanked 13 times in 13 posts
Location: Sydney

Test Date: ********
Target GMAT Score: 740
PostSun Jul 05, 2009 1:45 pm Reply with quote
Rahul,

can you explain how can you neglect 1 please?

Thanks,
Vikas

rahulg83 wrote:
Quote:
2) The value of 10^8 - 10^2/10^7 - 10^3 is closest to which of the following?

A. 1
B. 10
C. 10^2
D. 10^3
E. 10^4
i suppose question asks for value of (10^8 - 10^2)/(10^7 - 10^3), it can be written as 10^2{(10^6)-1}/10^3{(10^4)-1}, now 1 can be neglected in comparison with 10^6 or 10^4

So our expression will now reduce to (10^2*10^6)/(10^3*10^4)=10 ans..
Back to top
View user's profile Send private message Send e-mail
kath_the_great4
Just gettin' started!



Joined: 19 May 2008
Posts: 24

Thanks given: 2
Thanked 0 times in 0 posts

Target GMAT Score: 700
PostSun Jul 05, 2009 7:15 pm Reply with quote
1 is insignificant when you are dealing with numbers in the thousands...we are not looking for an exact response here.
Back to top
View user's profile Send private message
Display posts from previous:   

Post new topic   Reply to topic All times are GMT - 8 Hours
Page 1 of 1