problem on numbers

This topic has expert replies
Newbie | Next Rank: 10 Posts
Posts: 2
Joined: Thu Sep 12, 2013 3:52 am

problem on numbers

by twinkzz » Thu Sep 12, 2013 3:59 am
the sum of four consecutive multiples of 16 is 2048 more than the second number. what is the third number????


plzz answer :?

Master | Next Rank: 500 Posts
Posts: 468
Joined: Mon Jul 25, 2011 10:20 pm
Thanked: 29 times
Followed by:4 members

by vipulgoyal » Thu Sep 12, 2013 4:12 am
seems eager to get ans, posted thrice

here we go

16x + 16x+16 + 16x+32 + 16x+48 - 16x+16 = 2048
48x + 80 = 2048
x =41,
third no 16*41 + 32 = 688

GMAT/MBA Expert

User avatar
Elite Legendary Member
Posts: 10392
Joined: Sun Jun 23, 2013 6:38 pm
Location: Palo Alto, CA
Thanked: 2867 times
Followed by:511 members
GMAT Score:800

by [email protected] » Thu Sep 12, 2013 11:53 am
Hi twinkzz,

If this were a GMAT question (and I don't believe that it is), then the question would come with 5 answer choices. These answers would make solving the question considerably easier because:

1) The correct answer MUST be a multiple of 16
2) By testing an answer, you could backtrack, figure out the 1st, 2nd and 4th numbers and prove whether they fit the facts of the question or not.

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
Image

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2095
Joined: Tue Dec 04, 2012 3:22 pm
Thanked: 1443 times
Followed by:247 members

by ceilidh.erickson » Thu Sep 12, 2013 1:31 pm
I agree with Rich - this seems way too computation-heavy for a GMAT problem. Vipugoyal's solution is correct, but it's important to understand how we got there.

If we have 4 consecutive multiples of 16, then the first term is going to be 16 times some number, the second term will be 16 times the next biggest number, and so on.
16x + 16(x + 1) + 16(x + 2) + 16(x + 3)

We're told that the sum of these terms is equal to 2048 more than the second number (a real GMAT question would use "term" instead of "number"). Since the second term was 16(x + 1), we can say:
16x + 16(x + 1) + 16(x + 2) + 16(x + 3) = 2048 + 16(x + 1)

Subtract that 16(x + 1) from both sides, and simplify.

Now at this point, you'll have to do way more math than you'd ever do on a real GMAT problem to solve. I'd disregard this question... and other questions from whatever source it came from.

Just make sure you understand consecutive integer setup!
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education