Jumlah bilangan kelipatan 3 antara 200 dan 300 adalah

201 + 204 + 207 + ... + 294 + 297
a = 201
b = 3

Un = a + (n-1)b
297 = 201 + (n - 1)3
3n - 3 = 297 - 201
3n = 96 + 3
n = 99/3
n = 33

Sn = ⁿ/₂ (a + Un)
S₃₃ = ³³/₂ (201 + 297)
S₃₃ = ³³/₂ (498)
S₃₃ = 33 × 249
S₃₃ = 8.217

a=201
bagi angka dgn 3
u33=300
sn=1/2×33(2.201+(32)3)
=1/2×33(402+96)
=1/2×33(498)
=33×249
=8217