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probability again

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probability again

by jayanti » Fri Jul 29, 2011 7:35 am
if number N is randomly drawn from a set of all non-negative single digit integers what is the probability that 5N^3/8 is an integer
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by pemdas » Fri Jul 29, 2011 9:20 am
[spoiler]1/5[/spoiler]

including 0 (non-negative and non-positive) N can be 10 values
for 5N^3/8 to be an integer N must be an integer when N^1/8 as 5 is the prime number and the power of 3/8 cannot be further reduced. Hence N can be 0 and 1 only
so we get 2 good selections out of 10 possibilities or 1/5
jayanti wrote:if number N is randomly drawn from a set of all non-negative single digit integers what is the probability that 5N^3/8 is an integer
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by jayanti » Fri Jul 29, 2011 10:28 am
should it not be 1/2 as as the digit should be divisable by 8 to make it an integer.
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by ColumbiaVC » Fri Jul 29, 2011 2:10 pm
[spoiler]1/5[/spoiler]

(5/8)x(N^3)=int

For only N=0,2 from {0,1,2,...,9} the above condition is satisfied.
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by Bek » Fri Jul 29, 2011 7:50 pm
I got 1/2

All non-negative single digit integers: 0,1,2,3,4,5,6,7,8,9

5N^3/8 = integer

5*0^3/8 = 0
5*2^3/8 = 5
5*4^3/8 = 40
5*6^3/8 = 60
5*8^3/8 = 320

The probability that 5N^3/8 = an integer is 5/10 or 1/2
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by ntamhane » Fri Jul 29, 2011 8:15 pm
1/5 ans there are only 2 values that satisfy the condition 0 and 1.
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by Bek » Fri Jul 29, 2011 9:11 pm
Can explain how?

5N^3/8 =

5*0^3/8 = 0 this is integer
5*1^3/8 = 5/8 this is not integer
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by beatthegmat.garry » Sat Jul 30, 2011 1:51 pm
The quotient is not clear. Please use paranthesis where ever necessary

I see two kinds: (a) 5*(N^3)/8 (b) 5*N^(3/8)
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by Bek » Sat Jul 30, 2011 5:55 pm
nn
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by pemdas » Sun Jul 31, 2011 9:04 am
i think the poster made mistake in his post

it should be clarified either
==> 5*n^(3/8)

or

==> (5*n^3)/8
???
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by naveen451 » Mon Aug 01, 2011 2:22 am
ans is 1/2
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by bblast » Mon Aug 01, 2011 6:39 am
sample space is {0,1,2,3,4,5,6,7,8,9} = 10 numbers

for 5 * N cube to be divisible by 8, N must be divisible by 2


thus favorable cases - {0,2,4,6,8} - remember 0 is divisible by any integer. i.e 0/N = Integer (for all N).


required prob = 1/2
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by BABAMANALI » Mon Aug 01, 2011 11:36 pm
I'm a little confused. If non negatives are to be considered why are we including 0 in the sample space.
For me the answer is 4/9.
Expert help would be appreciated.
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by bblast » Mon Aug 01, 2011 11:48 pm
BABAMANALI wrote:I'm a little confused. If non negatives are to be considered why are we including 0 in the sample space.
For me the answer is 4/9.
Expert help would be appreciated.
Hi, always remember that 0 is neither positive nor negative.
0 is even.
0/any number = integer.
any number/0 = undefined.
0^0 is undefined - never test this case in DS
0! = 1
any number^0 = 1.
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by jayanti » Tue Aug 02, 2011 1:30 am
(5*n^3)/8 is the question
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