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I need explanation for 1000 PS question

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Source: — Problem Solving |

by llewellyn27 » Thu Jun 12, 2008 2:07 pm
I think the answer is 6

using the eqn 3n+4 (Let n = 1,2,3,4,5,6,7)

By process of elimination the answer is 6

Ex:

3*1 + 4 = 7
3*2 +4 = 10(Divisible by 5)
3*4 + 4 = 16 (Divisible by 4 and 8)

and so on till u get only 6 remaining


TOOK ME 2 MINS
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by babachal » Thu Jun 12, 2008 2:53 pm
i did not get it, sorry, look

3*4+4=16
3*5+4=19
3*6+4=22
3*7+4=25
3*8+4=28

now 5,7,and 8 can not be factor of the what from formula equal as well as 6, so how did you pick this number?
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by babachal » Thu Jun 12, 2008 3:04 pm
oh, sorry now i got it,

thank you!
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by Ian Stewart » Thu Jun 12, 2008 4:53 pm
You might also look at it this way: you can divide 3n+3 by 3 (it's equal to 3*(n+1)), so you definitely cannot divide 3n+4 by 3; you'll always get a remainder of 1, because it's one greater than a multiple of 3. If you can't divide 3n+4 by 3, you definitely can't divide it by 6, or any other multiple of 3.
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by rsesha » Thu Mar 11, 2010 10:22 am
[quote="babachal"]If n is an integer, which of the following CANNOT be a factor of 3n + 4 ?

(A) 4
(B) 5
(C) 6
(D) 7
(E) 8[/quote]

hi could you please send me a copy of 1000 ps and ds questions. Thanks
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by kstv » Thu Mar 11, 2010 10:50 am
n can be odd or even
if odd then n= 2a+1 where a is any no
so 3n + 4 = 6a + 7 when divided by 6 will leave a remainder 1 as 6a is divisible by 6
if even n = 2a
3n +4 = 6a = 4 where it will leave a remainder 1
1 1/2 year old Q
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