Question: A bag contains 7 blue balls and 5 yellow balls. If two balls are selected at random, then what is the probability that none is yellow?
Options:
A) $ \frac{5}{33} $
B) $ \frac{5}{22} $
C) $ \frac{7}{22} $
D) $ \frac{7}{33} $
E) $ \frac{7}{66} $
Show Answer
Answer:
Correct Answer: C
Solution:
- Total balls in the bag = 7 blue $ +5 $ yellow = 12 balls
Number of ways to choose 2 balls out of 12 $ ={}^{12}C _2 $
$ =\frac{12!}{2!10!}=\frac{12\times 11}{1\times 2}=66 $
P (no ball is yellow) = P (both balls are blue)
Number of selecting 2 blue balls
$ ={}^{7}C _2=\frac{7!}{2!5!}=\frac{7\times 6}{1\times 2}=21 $
$ \therefore $ Required probability $ =\frac{21}{66}=\frac{7}{22} $