Question

What is the sum of the geometric series 20 + 21 + 22 + 23 + 23 + 24 + … + 29?

a. 1,023
b. 511
c. 2,407
d. 1,012

Answer 1

1023

Explanation:

2^0+2^1+2^2+2^3+2^4+2^5+2^6+2^7+2^8+2^9

1+2+8+16+32+64+128+256+512=1023

Answer 2

Since the geometric series is not long we can pair up the number

20 + 29 = 49
21 + 28 = 49
22 + 27 = 49
23 + 26 = 49
24 + 25 = 49
Since we made 5 pairs of 49, the answer is 245. (49 x 5)