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How do I add numbers 119 through 220 quickly without a calculator?

 Aug 21, 2017
edited by Guest  Aug 21, 2017
 #1
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Note that we have

 

119 + 120 + 121 +  ..... +  218 + 219 + 220

 

We can rearrange this as

 

(119 + 220 )   + (120 + 219)  + ( 121 + 218) +  ........

 

Note that each pair sums to 339

 

And we have  [ 220 - 119 + 1] / 2  = 51 pairs

 

So....51 (339)  = 17,289

 

 

cool cool cool

 Aug 21, 2017

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