Question 1135819
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(1) There are 9+12=21 people in the group; you can choose any 3 of them.<br>
{{{C(21,3) = (21*20*19)/(3*2*1) = 1330}}}<br>
1330 different groups of 3 if there are no restrictions.<br>
(2) Now you have to choose 3 of the 9 boys AND 3 of the 12 girls.  The "AND" means you are going to multiply the two numbers to get the final answer.<br>
{{{C(9,3)*C(12,3) = 84*220 = 18480}}}<br>
18480 different groups of 6 consisting of 3 boys and 3 girls.