jumlah bilangan kelipatan 3 antara 100 dan 300 adalah...

Bab Barisan dan Deret
Matematika SMP Kelas VIII

102, 105, 108, ...., 297

a = 102
b = 3

Un = 297
a + (n - 1) b = 297
102 + (n - 1) . 3 = 297
(n - 1) . 3 = 297 - 102
n - 1 = 195 / 3
n = 65 + 1
n = 66

Sn = (n/2) . (a + Un)

S66 = (66/2) . (102 + 297)
S66 = 33 . 399
S66 = 13.167