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Suppose n is a two-digit positive integer with units digit 5
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09 Sep 2018, 19:44
09 Sep 2018, 19:44
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Suppose \(n\) is a two-digit positive integer with units digit 5, and tens digit u. Now, if \(E=\frac{(n^2-25)}{100}\), then express E in terms of u.
A. \(u+1\)
B. \(u^2+1\)
C. \(u^2-u\)
D. \(u^2+u\)
E. \(u^2+u+1\)
Here is how I did it:
E
=(n^2-25)/100
=[(n+5)(n-5)]/100
=[(u+1)*10*(u-1)*10]/100
=(u+1)(u-1)
=u^2-1, which is not an choice so I don't know where I did wrong.
A. \(u+1\)
B. \(u^2+1\)
C. \(u^2-u\)
D. \(u^2+u\)
E. \(u^2+u+1\)
Here is how I did it:
E
=(n^2-25)/100
=[(n+5)(n-5)]/100
=[(u+1)*10*(u-1)*10]/100
=(u+1)(u-1)
=u^2-1, which is not an choice so I don't know where I did wrong.
Re: Suppose n is a two-digit positive integer with units digit 5
[#permalink]
10 Sep 2018, 10:50
10 Sep 2018, 10:50
5
from the question, it can be said that n=10u+5.
now just plug it into the expression for E and then you'll get u^2+u after a little calculation.
answer D
now just plug it into the expression for E and then you'll get u^2+u after a little calculation.
answer D
General Discussion
Re: Suppose n is a two-digit positive integer with units digit 5
[#permalink]
10 Nov 2018, 07:25
10 Nov 2018, 07:25
answer must be D only
n = 10u+5
n = 10u+5
Re: Suppose n is a two-digit positive integer with units digit 5
[#permalink]
16 Nov 2018, 18:08
16 Nov 2018, 18:08
saifee wrote:
from the question, it can be said that n=10u+5.
now just plug it into the expression for E and then you'll get u^2+u after a little calculation.
answer D
now just plug it into the expression for E and then you'll get u^2+u after a little calculation.
answer D
Please provide clear explanation.
Re: Suppose n is a two-digit positive integer with units digit 5
[#permalink]
19 May 2019, 08:02
19 May 2019, 08:02
10U+5=n
So, E=[(10U+5)^2-25]/100
by calculation,E= U^2+U.
So, E=[(10U+5)^2-25]/100
by calculation,E= U^2+U.
GRE Prep Club Tests Editor
Joined: 13 May 2019
Affiliations: Partner at MyGuru LLC.
Posts: 186
Location: United States
GMAT 1: 770 Q51 V44
GRE 1: Q169 V168
WE:Education (Education)
Re: Suppose n is a two-digit positive integer with units digit 5
[#permalink]
19 May 2019, 08:46
19 May 2019, 08:46
1
Expert Reply
Quote:
Suppose \(n\) is a two-digit positive integer with units digit 5, and tens digit u. Now, if \(E=\frac{(n^2-25)}{100}\), then express E in terms of u.
A. \(u+1\)
B. \(u^2+1\)
C. \(u^2-u\)
D. \(u^2+u\)
E. \(u^2+u+1\)
A. \(u+1\)
B. \(u^2+1\)
C. \(u^2-u\)
D. \(u^2+u\)
E. \(u^2+u+1\)
Anytime you have a problem with variables in the choices and the problem, consider plugging in your own easy value(s) as an alternative to an often needlessly complex textbook algebraic approach. Easy values are going to be numbers that conform to the conditions of the problem, but are not themselves in the answer choices. In this case, I might consider plugging in n = 35, which in turn means that u = 3.
Subsequently, E = (35^2 - 25) / 100 = 12.
Now, plug u = 3 into each of the choices, testing all individually, seeking a match to the found value E = 12.
A. 3 + 1 ≠ 12 | Eliminate
B. 9 + 1 ≠ 12 | Eliminate
C. 9 - 3 ≠ 12 | Eliminate
D. 9 + 3 = 12 | Hold
E. 9 + 3 + 1 ≠ 12 | Eliminate
Select Choice D as the only match to the sought value of 12.
Re: Suppose n is a two-digit positive integer with units digit 5
[#permalink]
20 Sep 2021, 22:37
20 Sep 2021, 22:37
Hello from the GRE Prep Club BumpBot!
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Thanks to another GRE Prep Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).
Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
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