Question 1160920
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I will translate the statement to the Algebra language.



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Let M, A, J and S be the corresponding probabilities for each of the participant.


Then from the condition, you have this system of 4 equations

    M + A + J + S = 1    (1)

    M = 3A               (2)

    J = 2S               (3)

    M + J = 0.7          (4)


The translation is just completed.


Note that (4) is true since the events to win for M and for J are DISJOINT.



The rest is just technique, and I do not want to deprive you a joy to complete the solution on your own.
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