Răspuns:
Explicație pas cu pas:
a) 25+26+27+...+60=
60 - 25 + 1 = 36 termeni are suma
= 36 × ( 25+60) : 2 =
= 36 × 85 : 2 =
= 1 530
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b) 11+12+13+...+50=
50 - 11 + 1 = 40 termeni
= 40 × (11+50) : 2 =
= 20 × 61 =
= 1 220
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c) 21+22+23+...+70=
70 - 21 + 1 = 50 termeni
= 50 × (21+70) : 2 =
= 50 × 91 : 2 =
= 4 550 : 2 =
= 2 275
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d) 28+29+30+...+80=
80 - 28 + 1 = 53 termeni
= 53 × ( 28 + 80 ) : 2 =
= 53 × 108 : 2 =
= 2 862
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e) 76+77+78+...120=
120 - 76 + 1 = 45 termeni
= 45 × ( 76 + 120 ) : 2 =
= 45 × 196 : 2 =
= 4 410
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f) 98+99+100+...+210=
210 - 98 + 1 = 113 termeni
= 113 × ( 98 + 210 ) : 2 =
= 113 × 302 : 2 =
= 17 063
