Question 1034236
.
a railroad bridge is built over a v-shaped canyon. if the supports are 2 feet long at each end, the center support is 422 feet long, 
and the supports increase in length by 3 feet each support, what is the total length of all supports?
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There are {{{(422 - 2)/3}}} = 140 supports on one side with the lengths from 2 feet to 419 feet long, 
and there is the same amount of 140 supports on the other side. Plus one central support of 422 feet long.

Combine 

   2 +   5 +   8 + . . . + 419 + 422
+
 419 + 416 + 413 + . . . +   2

--------------------------------

 422 + 422 + 422 + . . . + 422 + 422


422 feet taken 141 times. You will get the combined length 422*141 = 59502 feet, in total.
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It is the "Gauss' method" for summing up an arithmetic progression.
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