Jumlah bilangan kelipatan 7 antara 102 dan 197 adalah

Pola 105, 112……196

U1 = 105 = a
beda = 7
Un = 197
Un = a + (n-1)b
196 = 105 + 7n – 7
196 = 7n + 98
98 = 7n
n = 14

S14 = 7 (210 + 13(7) = 2107

105, 112, 119, 126, …. , 182, 189, 196

Deret aritmatika

a = 105 b = 7

Un = a + (n – 1)b

196 = 105 + (n – 1) 7

196 – 105 = 7n – 7

7n = 91 + 7

7n = 98

n = 98 ÷ 7 = 14

Sn = (n ÷ 2) × ( a + Un)

= (14 ÷ 2) × (105 + 196)

= 7 × 301

= 2.107