Integers

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Integers

by masuarezdl » Sat Jan 31, 2009 12:36 pm
If n is a positive iteger and r is th remainder when n² - 1 is divided by 8, what is the value of r?

(1) n is odd.
(2) n is not divisible by 8.

When trying to use statement 1, as far s I see, all odd numbers have a remainder of 0. For example:
3² - 1 = 8, Quotient: 1, Remainder: 0
5² - 1 = 24, Quotient: 3, Remainder: 0
7² - 1 = 48, Quotient: 6, Remainder: 0
9² - 1 = 80, Quotient: 10, Remainder: 0
11² - 1 = 120, Quotient: 15, Remainder: 0
13² - 1 = 168, Quotient: 21, Remainder: 0
15² - 1 = 224, Quotient: 28, Remainder: 0

Any thoughts on this?
Source: — Data Sufficiency |

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by yalanand » Sat Jan 31, 2009 1:25 pm
Dont forget 1

1² - 1 = 0, Quotient: 0, Remainder: 0

Answer is D right ?

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by vikram_k51 » Sat Jan 31, 2009 1:27 pm
If n is a positive iteger and r is th remainder when n² - 1 is divided by 8, what is the value of r?

(1) n is odd.
(2) n is not divisible by 8.

Question Rephrase: r is th e remainder when (n+1)(n-1) is divided by 8.

1:n=odd;

For any odd value of n,the rem is always 0.Hence sufficient

2:n is not divisible by 8..here n can be anything 2,3,4,5,6,7 Each case will give a diff remainder when n² - 1 is divided by 8. Not Sufficient


Hence A

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by yalanand » Sat Jan 31, 2009 1:39 pm
Correct its A...sorry i read it as n divisible by 8...guess m sleepy now :)

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by masuarezdl » Sat Jan 31, 2009 1:43 pm
Yes, its A. You made it clear, thanks. Sometimes after doing so many problems we dont take a second look at the question.