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Suppose n is a two-digit positive integer with units digit 5

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Suppose n is a two-digit positive integer with units digit 5 [#permalink] New post 09 Sep 2018, 19:44
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Question Stats:

62% (01:38) correct 37% (02:09) wrong based on 8 sessions
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.
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Re: Suppose n is a two-digit positive integer with units digit 5 [#permalink] New post 10 Sep 2018, 10:50
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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
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Re: Suppose n is a two-digit positive integer with units digit 5 [#permalink] New post 10 Nov 2018, 07:25
answer must be D only
n = 10u+5
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Re: Suppose n is a two-digit positive integer with units digit 5 [#permalink] New post 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

Please provide clear explanation.
Re: Suppose n is a two-digit positive integer with units digit 5   [#permalink] 16 Nov 2018, 18:08
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Suppose n is a two-digit positive integer with units digit 5

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