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Ailinasan08
a fost răspuns

Calculati suma numerelor 3+8+13+18+....408

Răspuns :

3=3+5*0
8=3+5*1
13=3+5*2
......
408=3*5*81

S=3*82+5*(1+2+.....+81)
=246+5*81*82/2=246+16605=16851
102533

3+8+13+18+....408 = (3+408)·82:2 = 411·41 = 16851

(408-3):5 +1 = 82 termeni

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