### Brain Teasers

# 30 Numbers

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?

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?

### Hint

Try to find the pattern.### Answer

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.

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## Comments

from 30 terms it will go to 15 terms, and then to 8 terms, and then 4 terms and then to 2 terms, ultimately, there will only be 1 term.

like this puzzle!!!!!

like this puzzle!!!!!

you can express a new number as the sums of the previous ones and you'll eventually be left with the two numbers 137 and 328 or, (1+2+3+4+21+22+23+24+25+26+27+28+29+30) and (5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20) respectively, you'll then add these last 2 numbers and notice that you've just added the numbers 1-30.

Nice teaser. Different from those I already read.

Really Good one..

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