jumlah bilangan kelipatan 5 antara 100 dan 300 adalah...

300-100 = 5k+5
200-5 = 5k
195 = 5k
k = 195/5 = 39 (total angka)

S39 = 39/2 (2.105 + (39-1)5)
= 39/2 (210 + (38.5))
= 39/2 (210 + 190)
= 39/2 (400)
= 39 . 200
= 7800