What is the sum of first 40 terms of 1 + 3 + 4 + 5 + 7 + 7 + 10 + 9 + ….?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 1030
N = N1 + N2
N1 = (1 + 4 + 7 + 10.........)
N2 = (3 + 5 + 7 + 9..........)
N1 = 20/2[2 × 1 + (20 - 1) × 3] = 10[2 + 57] = 590
N2 = 20/2[2 × 3 + (20 - 1) × 2] = 10 × [6 + 38] = 440
N = N1 + N2 = 440 + 590 = 1030