edithvalencia1 edithvalencia1

29-09-2016
Mathematics

contestada

How will you rearrange the sum 1 + 2 + . . . + 20?

Respuesta :

apologiabiology apologiabiology

29-09-2016

notice, ending ends makes it easeier
1+20=21
2+19=21
...
10+11=21

there are 10 pairs of numbers
they add to 21
10 times 21=210

the sum is 210

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