## Que: If n is an odd integer, which of the following MUST BE an integer?

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### Que: If n is an odd integer, which of the following MUST BE an integer?

by [email protected] Revolution » Thu May 13, 2021 9:32 pm

00:00

A

B

C

D

E

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Que: If n is an odd integer, which of the following MUST BE an integer?

I. $$\frac{n^2-1}{2}$$

II. $$\frac{n-1}{2}$$

III. $$\frac{n}{2}$$

A. I only
B. II only
C. III only
D. I & II only
E. I, II, & III

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### Re: Que: If n is an odd integer, which of the following MUST BE an integer?

by [email protected] Revolution » Sat May 15, 2021 9:27 pm
Solution: Multi-Choice questions: ‘Must be’ VS ‘Could be’.

We have to find the options that must be true

‘MUST BE’: Choose only the options that are absolutely true in ALL cases

=> ‘n’ is an odd integer, Always an integer

=> n = odd = 2m+1 (m is always an integer)

I. $$\frac{n^2-1}{2}=\frac{\left[\left(2m+1\right)^2-1\right]}{2}=\frac{\left[4m^2+4m+1-1\right]}{2}=2m^2+m$$ => AN INTEGER ∴ Option is TRUE

II. $$\frac{n-1}{2}=\frac{\left[\left(2m+1\right)-1\right]}{2}=m$$ => AN INTEGER ∴ Option is TRUE

III. $$\frac{n}{2}=\frac{\left(2m+1\right)}{2}=m+0.5$$ => NOT AN INTEGER ∴ Option is NOT TRUE

Only options I and II are TRUE.

Therefore, D is the correct answer.