table has 4numbers(1...10).probability for table has 2 same "couple number" a.0,432 b.0,504 c.0,027 d.0.036

Answer 1

I think this means, pick 4 numbers from the set {1, 2, 3, ..., 10}. What is the chance that you pick exactly two numbers the same.

There are C(10,1) ways to pick the 'couple number'.
There are C(9,2) ways to pick the remaining two 'different' numbers.
There are C(4,2) ways to pick where the two 'different' numbers go.

C(10,1) = 10
C(9,2) = 36
C(4,2) = 12

C(n,r), the combination of n things taken r at a time is equal to:
n! / [r! * (n - r)!]

So there are 4320 combinations that have exactly two 'couple numbers', but there are a total of 10000 (10^4) combinations, so the probability of picking exactly two numbers the same is:

4320/10000 or 0.432

The answer is:
a. 0.432

Answer 2

I do not understand either but if it will help all the digits add up to nine in each number

Answer 3

I don't understand your question.