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Source: — Problem Solving |

by sk818020 » Fri May 07, 2010 12:13 pm
The answer is A, or as you put it "1.". When something is divisible by 5, the remainder when divided by five will be 0.
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by sk818020 » Fri May 07, 2010 12:34 pm
If its not a trick question and you meant to put divided by, not "divisible by". The following is what we can conclude;

[(3^1)+2]/5= 1 + 0/5
[(3^2)+2]/5= 2 + 1/5
[(3^3)+2]/5= 5 + 4/5
[(3^4)+2]/5= 16 + 3/5
[(3^5)+2]/5= 49 + 0/5
[(3^6)+2]/5= 146 + 1/5
[(3^7)+2]/5= 437 + 4/5
[(3^8)+2]/5= 1312 + 3/5
[(3^9)+2]/5= 3937 + 0/5

Obviously from this we can see that there is a pattern of 0, 1, 4, 3. The question tells us that were going to be raising 3 to an odd degree becaues 8n+3 tell us so. N times and even number will make that even. Any even number plus an odd number, 8n+3, will be an odd number. As you can see from the evidence above there are different remainders for different odd values of n. When n=1, remainder is 0. When n=3, remainder equals 4. We can conlude that the, when devided by 5 the number will have a remainder of 0 or 4.

We know that there is a pattern and that the remainder must be 0 or 4. We need to think about what were raising it to and what those number fall on.

When n=1, 8*1+3= 11
n=2, 8*2+3= 19
n=3, 8*3+3= 27

If we devide these numbers by four the remainder will tell us where on the pattern of , 0,1,4,3 we will be at. If the remainder of the power divided by 4 is 1, then the remainder of the number in general will be 0. If the remainder of the power divided by 4 is 2, then the remainder of the number in general will be 1. If the remainder of the power divided by 4 is 3, then the remainder of the number in general will be 4.
So ,

11/4=2+3/4
19/4=4+3/4
27/4=6+3/4

Seeing this we can conclude that the power will always be in the third position in the pattern, thus the remainder of the number in general will always be 4.
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by clock60 » Fri May 07, 2010 2:09 pm
pradeepkaushal9518 wrote:if n is a positive integer, what is the remainder when (3^8n+3) + 2 is divisible by 5 ?

1.0
2.1
3.2
4.3
5.4
agree with E-4

3^(8n+3)=3^3*3^8n

3^3=27=25+2 so remainder 2, when divide by 5

if n=1 then
3^8=....1
if n=2 then
3^16=.....1
so the same pattern with n=3,4...
....1=000+1 with remainder 1 when divide by 5

when we multiply remaiders from 3^3 and 3^8n=2*1=2
2=5*0+2 with remaider 2

and sum the remainders left after division
2+2=4
4=5*0+4
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by liferocks » Fri May 07, 2010 5:18 pm
Just wanted to put a quicker approach

3^(8n+3)+2=3*9^(4n+1)+2

when we divide 9 by 5 reminder is -1 and -1^(4n+1)=-1 as 4n+1 is odd

so when 3*9^(4n+1)+2 is divided by 5 reminder will be -3+2=-1 or reminder is 5-1=4
Ans option 5
"If you don't know where you are going, any road will get you there."
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