1+1+2+2+3+3+4+4+...+50+50
= ( 1+2+3+4+...+50 ) x 2
= 1275 x 2
= 2250
1+1+2+2+3+3+4+4+...+50+50
=2x1 + 2x2 + 2x3 + 2x4 + ...+ 2x50
=2x(1+2+3+4+...+50)
=2x 1275=2550
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1 + 1 + 2 + 2 + 3 + 3 + 4 + 4 + ... + 50 + 50
= ( 1 + 2 + 3 + 4 +... + 50 ) x 2
= 1275 x 2
= 2250