Question

Jumlah dari deret 7+11+15+19+23+........+103 adalah........
A. 1320
B. 1375
C. 2640
D. 3.400

Answer 1

B= 11-7=4
a= 7
Un= a+(n-1) b
103= 7+(n-1) 4
= 7+4n-4
=3+4n
103-3=4n
100=4n
n=100:4
n= 25
S25= 1/2n(a + Un)
= 1/2 ( 25)(7+103)
= 1/2 (25) (110)
= 25 x 55
=1.375(b)