Question

Qual soma dos múltiplos de 7
compreendidos entre 1 e 100?

(A) 735.
(B) 742.
(C) 728.
(D) 749.
(E) 746.​

Answer 1

a1 = 7

an = 98

r = 7

an = a1 + (n - 1)r

98 = 7 + (n - 1) × 7

(98 - 7)/7 + 1 = n

n = 91/7 + 1

n = 13 + 1

n = 14

Sn = (a1 + an) × n/2

S24 = (7 + 98) × 14/2

S24 = 105 × 7

S24 = 735

Resposta: (A) 735.