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# If 4 whole numbers taken at random are multiplied together,

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If 4 whole numbers taken at random are multiplied together, [#permalink]  04 Jun 2004, 20:08
If 4 whole numbers taken at random are multiplied together, what is the probability that the last digit in the product is 1,3,7 or 9?
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Mayur

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Re: Probability [#permalink]  04 Jun 2004, 20:33
abcd = 1, 3, 7, 9 (10)
or a, b, c, d <> 5 (10)

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hallelujah1234,
Thanks for the solution.
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Mayur

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hi helleujah, Can you explain the answer a bit more.

I was wondering a WHOLE NUMBER will include any valid integer and as such you can include a lot of numbers.

so how did you come to 10^4 as the possible combinations in 4 whole numbers. Did you consider only single digit positive whole numbers.
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I reason out as follows: -

Each of the digits 0,1,...,9 occur in 4 ways in the units digit (since we are multiplying 4 whole numbers). so, the total no. of ways = 10^4

Each of the digits 1,3,7,9 can occur in 4^4 ways.

So the prob. = 4^4/10^4.

Correct me if I am wrong.
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