Brain Teasers Optical Illusions Puzzle Hunts Codes & Ciphers Mechanical Puzzles
Personal Links
Browse Teasers
Search Teasers

30 Numbers

Math brain teasers require computations to solve.


Puzzle ID:#48749
Fun:*** (2.7)
Difficulty:** (2)
Submitted By:shenqiangAcn****!!
Corrected By:topnotch54




Numbers from 1 to 30 are written on a blackboard.

Add the first two numbers, and append it to the end, then erase the first two numbers.

For example, after the first time, the numbers become 3, 4, 5, ..., 29, 30, and 3.

Repeat this process until you get only one number.

How many addition operations are there, and what is the last number on the blackboard?

Open Calculator


After each operation, the numbers reduce by one, therefore you need 29 times.

Of course, the last number remaining on the blackboard is the sum of all the numbers from 1 to 30, which is (1+30)*30/2=465.


What Next?


See another brain teaser just like this one...

Or, just get a random brain teaser

If you become a registered user you can vote on this brain teaser, keep track of
which ones you have seen, and even make your own.


Back to Top

Online Now
5 users and 553 guests

Users In Chat
Follow Braingle!
Fold 'N Fly Paper Airplanes
Easy to follow folding instructions and videos.
Copyright © 1999-2017 | FAQ | Widgets | Links | Green | Subscribe | Contact | Privacy | Conditions | Advertise | Braingle Time: 12:11 am
Sign In Create a free account