The prompt should make it clear that each ball has either a red stripe or no stripe, as follows:
There are 1,200 golf balls in a golf ball dispensing machine. Each of the golf balls in the machine has either a red stripe or no stripe. If a ball is chosen at random, the probability that the ball has a red stripe is 1/9th the probability that the ball has no stripe. How many of the golf balls in the dispensing machine have a red stripe?
a)108
b)120
c)150
d)251
e)320
The probability that the ball has a red stripe is 1/9th the probability that the ball has no stripe.
In other words, the number of balls with no stripe is 9 times the number of balls with a red stripe.
Implication:
There are 9 balls with no stripe for every 1 ball with a red stripe.
Thus, of every 10 balls, 1 will have a red stripe, implying that the balls with a red stripe constitute 1/10 of the total number of balls:
(1/10)(1200) = 120.
The correct answer is
B.
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