# Aptitude - Numbers - Discussion

Discussion Forum : Numbers - General Questions (Q.No. 100)

100.

2 + 2

^{2}+ 2^{3}+ ... + 2^{9}= ?Answer: Option

Explanation:

This is a G.P. in which a = 2, r = |
2^{2} |
= 2 and n = 9. |

2 |

S_{n} = |
a(r^{n} - 1) |
= | 2 x (2^{9} - 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.

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.

It's simple.

Nilesh said:
8 years ago

Help me please why (r-1) take?

Post your comments here:

Quick links

Quantitative Aptitude

Verbal (English)

Reasoning

Programming

Interview

Placement Papers