# A level probability maths

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#1
I have this question and I got part a but I am confused where to start on question b
The probability distribution of a discrete random variable X is given by:

P(X = r) = k(6r2 −r3) for r = 1, 2, 3, 4, 5
P(X = r) = 0 otherwise
(a) Show that k = 1/105
Two values of X are chosen at random.
(b) Find the probability that the product of the two values is even.
0
3 months ago
#2
(Original post by Magicmanzb)
I have this question and I got part a but I am confused where to start on question b
The probability distribution of a discrete random variable X is given by:

P(X = r) = k(6r2 −r3) for r = 1, 2, 3, 4, 5
P(X = r) = 0 otherwise
(a) Show that k = 1/105
Two values of X are chosen at random.
(b) Find the probability that the product of the two values is even.
You could list (tree/grid) the outcomes/probability of the product of two values and sum the ones that are even. Or do 1-odd probability.
Last edited by mqb2766; 3 months ago
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#3
(Original post by mqb2766)
You could list (tree/grid) the outcomes/probability of the product of two values and sum the ones that are even. Or do 1-odd probability.
Thank you but how do I work out the values of X?
0
3 months ago
#4
(Original post by Magicmanzb)
Thank you but how do I work out the values of X?
If you draw a tree, for instance, you have to consider the different values it can take (as with most probability problems).
If you consider only the pair's that generate even or odd, it cuts down the options a bit.
Last edited by mqb2766; 3 months ago
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#5
(Original post by mqb2766)
If you draw a tree, for instance, you have to consider the different values it can take (as with most probability problems).
If you consider only the pair's that generate even or odd, it cuts down the options a bit.
So do I use the numbers 1-5 on the tree?
0
3 months ago
#6
(Original post by Magicmanzb)
So do I use the numbers 1-5 on the tree?
Those are the outcomes with a nonzero probability for one score.

A bit of thinking about the question may give an efficient way to get the final probability using even/odd, but failing that, just list the individual probabilities.
Last edited by mqb2766; 3 months ago
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