Leave the calculator alone to deduce the missing digit

The key to a speedy solution is to realise that all factorials greater than 5! must be divisible by 9 (because 3 and 6 are factors of 6! and 3x6=18, which...

The key to a speedy solution is to realise that all factorials greater than 5! must be divisible by 9 (because 3 and 6 are factors of 6! and 3x6=18, which is a multiple of 9).

Now, it is well known that every number divisible by 9 has its digit-sum also divisible by 9. So we simply need to add up the eighteen digits that have been given, to arrive at 52. Then, the unidentified, leftmost digit must have been 2, to make a grand total - divisible by 9 - of 54.

Hence the full integer is 2,432,902,008,176,640,000

Try more puzzlers >>

Go to the homepage >>

This was last published in May 2009

Read more on IT strategy

Start the conversation

Send me notifications when other members comment.

Please create a username to comment.

-ADS BY GOOGLE

SearchCIO

SearchSecurity

SearchNetworking

SearchDataCenter

  • How do I size a UPS unit?

    Your data center UPS sizing needs are dependent on a variety of factors. Develop configurations and determine the estimated UPS ...

  • How to enhance FTP server security

    If you still use FTP servers in your organization, use IP address whitelists, login restrictions and data encryption -- and just ...

  • 3 ways to approach cloud bursting

    With different cloud bursting techniques and tools from Amazon, Zerto, VMware and Oracle, admins can bolster cloud connections ...

SearchDataManagement

Close