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calculati urmatoarele sume 5+10+15+20+......+2020 va rog mult

Răspuns :

formula s=n(n+1):2
numitorul comun este 5
2020:5=404 n=404
s=404(404+1):2=163620:2=81810
81810*5=409050
5+10+15+........+2020     2020:5=404

S=5+19+15+.....+404
S=(5+2020).404:2
S=2025.404:2
S=818.100:2
S=409.050