How to solve factorials - Shortcut?

[beater]

Could one of you please explain a time effective method to solve factorials. For eg: How would you go about solving 30!

Thanks

[VP_Jim]

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.

[stop@800]

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.

[beater]

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!

[MediatorOfDeath]

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!

[Brent@GMATPrepNow]

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