What is the sum of the first twenty terms that are in both series 3 + 7 + 11 + 15 + ... and 1 + 6 + 11 + 16 + ...
+37157 S1 3 7 11 15 19 23 27 31 35 39 43 47 51
S2 1 6 11 16 21 26 31 36 41 46 51
makes a new series 11 31 51 a = 11 d = 20
S = (n/2) × (2a + (n−1)d)
S20 = 20/2 ( 2(11)+19(20))
= 10 (22+ 380) = 10(402) = 4020
+37157 S1 3 7 11 15 19 23 27 31 35 39 43 47 51
S2 1 6 11 16 21 26 31 36 41 46 51
makes a new series 11 31 51 a = 11 d = 20
S = (n/2) × (2a + (n−1)d)
S20 = 20/2 ( 2(11)+19(20))
= 10 (22+ 380) = 10(402) = 4020
