BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

How to solve factorials - Shortcut?

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |
GMAT Instructor
Posts: 1223
Joined: Thu May 01, 2008 3:29 pm
Location: Los Angeles, CA
Thanked: 185 times
Followed by:15 members

by VP_Jim » Sun Sep 21, 2008 12:35 pm
You'd never have to calculate 30! (or anything even close to it) on the GMAT. It's good to know the factorials up to, say, 5!, though.

Remember: the vast majority of the time, the GMAT does NOT test your computational abilities. If you find yourself doing lots of math, you're probably doing something wrong.
Jim S. | GMAT Instructor | Veritas Prep
Top
User avatar
Legendary Member
Posts: 871
Joined: Wed Aug 13, 2008 7:48 am
Thanked: 48 times

by stop@800 » Sun Sep 21, 2008 1:07 pm
Where are you required to solve this factorial?

The question must be expecting you to extract something from this number like units place or no of zeros or something else that can be obtained without calculating the value.
Top
Master | Next Rank: 500 Posts
Posts: 301
Joined: Tue Apr 22, 2008 6:07 am
Thanked: 2 times

by beater » Sun Sep 21, 2008 3:27 pm
I did not come across a question that required solving for 30!. But, I was just curious if there was a shortcut to solve factorials. Thanks!
Top
User avatar
Newbie | Next Rank: 10 Posts
Posts: 1
Joined: Sun Apr 14, 2013 5:44 pm

by MediatorOfDeath » Sun Apr 14, 2013 5:49 pm
There is a shortcut to finding factorials. It lets you do about half of the work, and get the same answer. I just recently discovered it, and made a website to put it on. Here is the link. If you are looking for speed, I would use the first method I share, and not worry about the second. Enjoy! :)
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pm
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1268 members
GMAT Score:770

by Brent@GMATPrepNow » Mon Apr 15, 2013 4:22 am
As VP_Jim mentioned, the GMAT will never require you to perform such a series of tedious calculations. However, when dealing with the combination formula, nCr = n!/(r!)(n-r!), you will have to work with several factorials. In these cases, there is a nice shortcut that will allow you to calculate combinations (like 12C3) in your head.

Here's our free video on this topic: https://www.gmatprepnow.com/module/gmat-counting?id=789

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Post new topic Post Reply
• Page 1 of 1