Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 04 Jul 2015, 06:39

### 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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# The fastest way?.

Author Message
TAGS:
Senior Manager
Joined: 14 Aug 2006
Posts: 365
Followers: 1

Kudos [?]: 5 [0], given: 0

The fastest way?. [#permalink]  12 Dec 2006, 18:43
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
The fastest way?..
Attachments

800_3.GIF [ 11.88 KiB | Viewed 503 times ]

Senior Manager
Joined: 23 Jun 2006
Posts: 387
Followers: 1

Kudos [?]: 311 [0], given: 0

the fastest way? not sure....
i used pythagoras theorem twice...

however, to save calculation time, i divided everything by 4.
(so the sides are 3,4,5). now, some of you know by heart that 3^2+4^2=5^2 (the most known example)...
so 3 and 4 gives 5.

5 and 5 gives 5*sqrt(2). or you may now by heart (another common example) that 1 and 1 give sqrt(2). so divide by 5.

so after first dividing by 4, then dividing by 5 we get sqrt(2) then the answer is 20*1.41 ~28

you could of course use just one step, knowing that in three dimensional space l^2 = a^2+b^2+c^2

but why bother remembering so much stuff...

however - the key to fast calculation, in my view, is breaking stuff into known and recognizable patterns, do the fast calculations on them, then transform it back.

!!!!better 10 fast and easy steps than 1 complicated step.!!!!

this at least was (and still is) my way of approaching stuff.

amit.
Senior Manager
Joined: 08 Jun 2006
Posts: 341
Location: Washington DC
Followers: 1

Kudos [?]: 26 [0], given: 0

Yes 28

D = sqrt(16^2 + 12^2 + 20^2) = sqrt (800) = sqrt(400 * 2) = 20 sqrt2
= 20 * 1.41.. > 28
Senior Manager
Joined: 14 Aug 2006
Posts: 365
Followers: 1

Kudos [?]: 5 [0], given: 0

I used the formula :

OA is 28

Thanks!
SVP
Joined: 08 Nov 2006
Posts: 1560
Location: Ann Arbor
Schools: Ross '10
Followers: 13

Kudos [?]: 169 [0], given: 1

hobbit wrote:
the fastest way? not sure....
i used pythagoras theorem twice...

however, to save calculation time, i divided everything by 4.
(so the sides are 3,4,5). now, some of you know by heart that 3^2+4^2=5^2 (the most known example)...
so 3 and 4 gives 5.

5 and 5 gives 5*sqrt(2). or you may now by heart (another common example) that 1 and 1 give sqrt(2). so divide by 5.

so after first dividing by 4, then dividing by 5 we get sqrt(2) then the answer is 20*1.41 ~28

you could of course use just one step, knowing that in three dimensional space l^2 = a^2+b^2+c^2

but why bother remembering so much stuff...

however - the key to fast calculation, in my view, is breaking stuff into known and recognizable patterns, do the fast calculations on them, then transform it back.

!!!!better 10 fast and easy steps than 1 complicated step.!!!!

this at least was (and still is) my way of approaching stuff.

amit.

In doing such questions, I have noticed that we would often need to figure out the length of the longest diagonal of the cube.

I simply do this.

length=sqrt[(longestside^2)+(sqrt(sum of squares of the other 2 sides))^2]

It's still the same formulae, but just that I dont bother about visualizing or drawing the cube.
_________________

My Profile/GMAT/MBA Story
http://www.gmatclub.com/forum/111-t59345

GMAT Club Premium Membership - big benefits and savings

Senior Manager
Joined: 20 Feb 2006
Posts: 373
Followers: 1

Kudos [?]: 7 [0], given: 0

C - 28

I used ratios 3:4:5 then x:x:x(sqrt(2))
Manager
Joined: 18 Nov 2006
Posts: 125
Followers: 1

Kudos [?]: 0 [0], given: 0

C

12, 16 >> 20
20,20 >>sqrt2 * 20 = 1.414 *20 =apprx 28
Senior Manager
Joined: 05 Oct 2006
Posts: 267
Followers: 1

Kudos [?]: 6 [0], given: 0

Re: PS - rod [#permalink]  15 Dec 2006, 21:10
basically the q is asking the length of the diagnonal in a 3-d frame.for which u have to take the diagonal of one face(Sqrt(a^2+b^2)=d
and then the diagonal of d and the 3rd side c.

in nutshell,find sqrt(a^2+b^2+c^2)

which is 20sqrt2 = 28
Re: PS - rod   [#permalink] 15 Dec 2006, 21:10
Similar topics Replies Last post
Similar
Topics:
5 What is the units digit of 13^4*17^2*29^3? 4 17 Oct 2010, 11:50
What is fastest way to solve this type of problem 2 15 Oct 2010, 23:23
fastest way to solve this ratio PS 1 02 Nov 2007, 17:03
Can anyone tell me the fastest approach to such questions 1 29 Oct 2007, 21:17
fastest way to solve this median problem- gmat prep PS 6 04 Oct 2007, 19:33
Display posts from previous: Sort by