KPK 3 dan 5 = 15
kelipatan 15 antara 200 dan 400 adalah 210, 225, .......... 390
a = 210
b = 15
Un = a + (n - 1) b
390 = 210 + ( n - 1 ) 15
390 - 210 = 15n - 15
180 = 15n - 15
180 + 15 = 15n
195 = 15n
n = 195/15
n = 13
Sn = n/2 ( 2a + ( n - 1 )b )
S13 = 13/2 ( 2 x 210 + ( 13 - 1 ) 15 )
= 13/2 ( 420 + ( 12 ) 15 )
= 13/2 ( 420 + 180 )
= 13/2 ( 600 )
= 3.900 ( B )
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KPK 3 dan 5 = 15
kelipatan 15 antara 200 dan 400 adalah 210, 225, .......... 390
a = 210
b = 15
Un = a + (n - 1) b
390 = 210 + ( n - 1 ) 15
390 - 210 = 15n - 15
180 = 15n - 15
180 + 15 = 15n
195 = 15n
n = 195/15
n = 13
Sn = n/2 ( 2a + ( n - 1 )b )
S13 = 13/2 ( 2 x 210 + ( 13 - 1 ) 15 )
= 13/2 ( 420 + ( 12 ) 15 )
= 13/2 ( 420 + 180 )
= 13/2 ( 600 )
= 3.900 ( B )