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PR - sequences

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PR - sequences

by jayhawk2001 » Mon May 28, 2007 2:16 pm
Interesting question. OA after a few reply.

A bowl is filled with consecutively numbered tiles from 1 to x. Joe pulls out a tile and uses it to construct Sequence Q, which consists of 10 consecutive integers starting with the number drawn. If Joe then selects one number from Sequence Q, what is the probability that the selected number is a multiple of 3?

(1) The last number in Sequence Q is a prime number that is less than 20.

(2) x<=10
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by Neo2000 » Mon May 28, 2007 7:58 pm
From statement 1 alone
If it ends in a prime number possible endings are 11,13,17,19

In each case, probability of picking a number such that it is a multiple of 3 = 3/10

Statement 2 really doesnt give you anything new or helpful

Hence Statement 1 alone
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by mendiratta » Wed May 30, 2007 3:14 am
I think it should be D.
1)
Rightly said above,
If it ends in a prime number possible endings are 11,13,17,19
so in all the above cases the starting number has to be 2,4,8 & 10 respectively.
so the probability is 0/4 = 0.
2)
if x<=10, then the number has to be 1 otherwise we cannot form series of 10 numbers.
in this case also probability = 0.

What is OA?
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by jayhawk2001 » Wed May 30, 2007 12:23 pm
mendiratta wrote:I think it should be D.
1)
Rightly said above,
If it ends in a prime number possible endings are 11,13,17,19
so in all the above cases the starting number has to be 2,4,8 & 10 respectively.
so the probability is 0/4 = 0.
2)
if x<=10, then the number has to be 1 otherwise we cannot form series of 10 numbers.
in this case also probability = 0.

What is OA?
OA is A.

mendiratta, I made the same mistake :-). We are given x <=10. The
sequence Q however is not bound to 10. So, you can technically take
x = 3 and form a sequence 3...12 or take x = 7 and form
sequence 7...16. Each sequence has a different number of multiples of
3s. Hence (2) is not sufficient.
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by mendiratta » Wed May 30, 2007 8:02 pm
my baddd....
:evil:
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