tentukan jumlah semua bilangan asli antara 1 sampai 100 yang habis dibagi 3

Mapel: Matematika
Bab: Barisan dan Deret

barisannya: 3, 6, 9, 12,..... 99
a = 3
b = 6-3 = 3

 jumlah n : Un = a + (n -1) b
                  99 = 3 + (n-1)3
                  99 = 3 + 3n -3
                  99 =  3n
                   n = 99/3
                   n =  33
jumlah semua bilangan S30 = n/2 (2a + (n-1)b)
                                             = 30/ 2 (2.3 + (33-1)3)
                                             = 15 (6 + 32(3))
                                              = 15 (6 + 96)
                                              = 15 (102)
                                              = 1530