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Bil pertama kelipatan 7 : 203
Bil terakhir kelipatan 7 : 399
Beda antar bilangan = 7
Banyak bilangan kelipatan 7
Un = a + bn - b
n = (un - s + b)/7
n = (399- 203 + 7)/7
n = 29 bilangan
Jumlah kelipatan 7
S29= n/2 (a + un)
S29 = 29/2 (203 + 399)
S29 =8729
Cari Jumlah seluruh bilangan dr 200-400
Banyak bilangan :
n = (400 - 200 + 1)/1
n = 201 bilangan.
S201 =201/2. (200 + 400)
S201 =24120
Maka jumlah bilangan yg bukan kelipatan 7
= 24120 - 8729
=15.391