Question 1083442
There are 21 cars and 10 will be displayed. Order doesn't matter so it is 21C10 for number of ways (denominator of probability)=352716.
4 cars chosen from 7 red is 7C4.  That is multiplied by 9C6, which is the number of ways to choose 6 cars from 9, which is 84
7C4=35.
Probability is 35*84/352716=2940/352716.  We multiply, because each of the first can be paired with any of the second.
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For 5 red and 5 black it is 7C5*1, since all black cars will be chosen.  This has a probability of  21/352716
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For 7 cars to be red it is 7C7*14C3, since there are 84 ways the other 3 cars may be chosen.  This gives a probability of 84/352716.