Browse Teasers
Search Teasers

## 30 Numbers

Math brain teasers require computations to solve.

 Puzzle ID: #48749 Fun: (2.75) Difficulty: (2.04) Category: Math Submitted By: shenqiang 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?

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.

Hide

## 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.