In a stack of cards, 9 cards are blue and the rest are red. If 2 cards are to be chosen at random from the stack without replacement, the probability that the cards chosen will both be blue is 6/11. What is the number of cards in the stack?
Choose one
A) 10
B) 11
C) 12
D) 15
E) 18
9/(9+x)∗8/(8+x)=6/119/(9+x)∗8/(8+x)=6/11   0=17x+x2−600=17x+x2−60   0=(x+20)(x−3)0=(x+20)(x−3)   x=3   9+3= 
<gadget id="calculator">9+3</gadget>
<output>12</output>
12   the answer is (12)
<result>C</result>
In a stack of cards, 9 cards are blue and the rest are red. If 2 cards are to be chosen at random from the stack without replacement, the probability that the cards chosen will both be blue is 6/11. What is the number of cards in the stack?