Răspunsuri

2014-10-09T01:10:04+03:00
1+2+3+...+50=50*51/2=1275
5+6+7+8+...+55=1+2+3+4+5+6+...+55-1-2-4=55*56/2-1-2-3-4=1530
10+11+12+...60=1+2+3+4+5+6+7+8+9+10+11+...+60-1-2-3-4-5-6-7-8-9=60*61/2-9*10/2=1830-45=1785
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