BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

sequence of two

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 123
Joined: Mon Feb 07, 2011 12:11 pm
Followed by:1 members

sequence of two

by rupsk » Sat Jul 09, 2011 7:27 am
S is the infinite sequence S1 = 2, S2 = 22, S3 = 222,...Sk = Sk-1 + 2(10k-1). If p is the sum of the first 30 terms of S, what is the eleventh digit of p, counting right to left from the units digit?

1
2
4
6
9

Please help me.
Top
Source: — Problem Solving |
User avatar
Master | Next Rank: 500 Posts
Posts: 461
Joined: Tue May 10, 2011 9:09 am
Location: pune
Thanked: 36 times
Followed by:3 members

by amit2k9 » Sat Jul 09, 2011 10:06 am
s4= 2222
thus 2+22+222 means units place sum = 2*3
tens place sum = 2*2
and hundreds place sum = 2*1.

using the same concept and the carry overs

units place (1st) = 2*30 = 60
tens place (2nd)= 2*29+6(carry over) ...
fifth place (5th)= 2*26+5
............
............
9th place = 2*22+4
11th palce = 2*20+4

thus 4 it is.
For Understanding Sustainability,Green Businesses and Social Entrepreneurship visit -https://aamthoughts.blocked/
(Featured Best Green Site Worldwide-https://bloggers.com/green/popular/page2)
Top
Master | Next Rank: 500 Posts
Posts: 123
Joined: Mon Feb 07, 2011 12:11 pm
Followed by:1 members

by rupsk » Sat Jul 09, 2011 12:01 pm
This is normal arithmetic way but is there any faster way?
Top
Post new topic Post Reply
• Page 1 of 1