# Aptitude - Numbers - Discussion

Discussion Forum : Numbers - General Questions (Q.No. 100)
100.
2 + 22 + 23 + ... + 29 = ?
2044
1022
1056
None of these
Explanation:

 This is a G.P. in which a = 2, r = 22 = 2 and n = 9. 2 Sn = a(rn - 1) = 2 x (29 - 1) = 2 x (512 - 1)   = 2 x 511   = 1022. (r - 1) (2 - 1)

Discussion:
7 comments Page 1 of 1.

Darla said:   2 years ago
@Pawan.

An arithmetic sequence has a constant difference between each term- 2, 4, 6, 8, 10, 12.

Here, all are added by 2 whereas geometric sequence has a constant ratio ie, multiplier between each term- 2, 4, 8, 16, 32. Here, all are multiplied by 2.

Pawan said:   2 years ago
How can you say that it's GP? Explain please.

Maneesha said:   3 years ago
Geometric Progress.

DONKUPAR LYNNONG said:   3 years ago
What is the full form of G. P?

Mohit bansal said:   7 years ago
Any other method? Not by direct multiplying or gp, in search of any other method to this type of questions.

Pari said:   8 years ago
2+4+8+16+32+64+128+256+512 = 1022.

It's simple.

Nilesh said:   8 years ago
Help me please why (r-1) take?