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30 Numbers

Math brain teasers require computations to solve.

 

Puzzle ID:#48749
Fun:*** (2.7)
Difficulty:*** (2.12)
Category:Math
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?

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Comments

averageguy
May 27, 2011

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!!!!!
averageguy
May 27, 2011

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.
pating**
May 31, 2011

Nice teaser. Different from those I already read.
SRB_1807Ain*
Aug 16, 2011

Really Good one..



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