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2 DS questions

by ocean » Sat Jan 03, 2009 3:49 am
Can you help me with these ones?:

"If n is a positive integer and r is the remainder when 4+7n is divided by 3, what is the value of r?"

(1) n+1 is divisible by 3
(2) n > 20.

and:

"If x and y are integers greater than 1, is x a multiple of y?"

(1) 3y^2 + 7y = x
(2) x^2 - x is a multiple of y.

thanks,
ocean
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Source: — Data Sufficiency |
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by mental » Sat Jan 03, 2009 6:30 am
A request: Try to post one question per post. That makes it easy to follow.

Ques 1: 4+7n is divided by 3

we can write it as, (3+1)+(6n+n) = 3 + 6n + n + 1
3 and 6n will be divisible by 3, remainder will be zero
we have to concentrate on (n+1)

st1: n+1 is divisible by 3, what we are looking for: Sufficient

st2: n>20: n=22, remainder of 23/3 = 2
n=23, remainder of 24/3 = 0: Insufficient

ANs: A
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by mental » Sat Jan 03, 2009 6:32 am
Ques 2 has been posted recently
pls search the forum
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by ocean » Sat Jan 03, 2009 9:46 am
hi mental,

how can "4+7n is divided by 3" be rewritten as "(3+1)+(6n+n)"? (How do you come from the first to the secon term?)

ocean

P.S.: sorry for the bad post!
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by cramya » Sat Jan 03, 2009 9:52 am
how can "4+7n is divided by 3" be rewritten as "(3+1)+(6n+n)"? (How do you come from the first to the secon term?)
7n = 6n+n
4 = 3+1

6n+n+3+1 can be rearranged as

(n+1) + (6n+3)

Stmt I

n+1 is divisible by 3. 6n is divisible by 3 and 3 is divisible by 3

Whenever u add terms that are each divisible by a number then the sum is also divisible by that number.

So the expression (n+1) + (6n+3) is always divisible by 3 with a remainder 0

One defnite value for remainder hence SUFF


Stmt II

n> 20

n=21

7n+4 = 151 gives a remainder of 1 when divided by 3

n=23

7n+4 = 165 when divided by 3 gives a remainder 0

2 different answers(more different answers possible based on n value) INSUFFICIENT

Choose A)
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by cramya » Sat Jan 03, 2009 9:53 am
Q2:

Refer here:

https://www.beatthegmat.com/multiple-que ... 23076.html
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