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A)5+ 10 +15 +.... +200=

Răspuns :

[tex]\displaystyle 5+10+15+...+200=5(1+2+3+...+40)=5 \times \frac{40(40+1)}{2} = \\ \\ =5 \times \frac{40 \times 41}{2} =5 \times \frac{1640}{2} =5 \times 820=4100[/tex]

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