If m is 2-digit positive integer and n is a positive integer, what is the units digit of (2^n)(m)(5^n)?
1) m=17
2) n=3
If m is 2-digit positive integer and n is a positive integer
This topic has expert replies
- Max@Math Revolution
- Elite Legendary Member
- Posts: 3991
- Joined: Fri Jul 24, 2015 2:28 am
- Location: Las Vegas, USA
- Thanked: 19 times
- Followed by:37 members
Math Revolution
The World's Most "Complete" GMAT Math Course!
Score an excellent Q49-51 just like 70% of our students.
[Free] Full on-demand course (7 days) - 100 hours of video lessons, 490 lesson topics, and 2,000 questions.
[Course] Starting $79 for on-demand and $60 for tutoring per hour and $390 only for Live Online.
Email to : [email protected]
- Max@Math Revolution
- Elite Legendary Member
- Posts: 3991
- Joined: Fri Jul 24, 2015 2:28 am
- Location: Las Vegas, USA
- Thanked: 19 times
- Followed by:37 members
==> In the original condition, you get 2 variables(m,n) and the answer is C. However, since this is an integer problem, a key question, if you apply CMT 4(A), when you solve 2), the first digit of (2^3)(m)(5^3) is always 0, so suffi. The answer is B.
Answer B
Answer B
Math Revolution
The World's Most "Complete" GMAT Math Course!
Score an excellent Q49-51 just like 70% of our students.
[Free] Full on-demand course (7 days) - 100 hours of video lessons, 490 lesson topics, and 2,000 questions.
[Course] Starting $79 for on-demand and $60 for tutoring per hour and $390 only for Live Online.
Email to : [email protected]
-
- Newbie | Next Rank: 10 Posts
- Posts: 2
- Joined: Sun Oct 02, 2016 6:11 pm
So isnt (2^n)m(5^n) same as (10^n)m.
Since n is a positive integer so n>=1, m is always multiplied by 10 and m is also an integer. So units digit is always 0. We dont really need m or n for the answer.
where am I going astray here in this thinking
Since n is a positive integer so n>=1, m is always multiplied by 10 and m is also an integer. So units digit is always 0. We dont really need m or n for the answer.
where am I going astray here in this thinking
-
- Newbie | Next Rank: 10 Posts
- Posts: 2
- Joined: Sun Oct 02, 2016 6:11 pm
GMAT/MBA Expert
- Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
You're absolutely correct, gmathundredgmathundred wrote:So isnt (2^n)m(5^n) same as (10^n)m.
Since n is a positive integer so n>=1, m is always multiplied by 10 and m is also an integer. So units digit is always 0. We dont really need m or n for the answer.
where am I going astray here in this thinking
(2^n)(m)(5^n) = (10^n)(m)
Since n is a positive integer, 10^n can equal 10, 100, 1000, 10000, 100000, etc
Since m is also a positive integer, we can be certain that the units digit of (10^n)(m) will be zero.
So, as you suggested, this question can be answered without using the statements.
As such, this would never be an actual GMAT question.
Cheers,
Brent
- Max@Math Revolution
- Elite Legendary Member
- Posts: 3991
- Joined: Fri Jul 24, 2015 2:28 am
- Location: Las Vegas, USA
- Thanked: 19 times
- Followed by:37 members
Hi all,
There has been a mistake.
It is supposed to be "n is an integer" and "positive" should be omitted.
Thank you.
There has been a mistake.
It is supposed to be "n is an integer" and "positive" should be omitted.
Thank you.
Math Revolution
The World's Most "Complete" GMAT Math Course!
Score an excellent Q49-51 just like 70% of our students.
[Free] Full on-demand course (7 days) - 100 hours of video lessons, 490 lesson topics, and 2,000 questions.
[Course] Starting $79 for on-demand and $60 for tutoring per hour and $390 only for Live Online.
Email to : [email protected]