Question

If I pick a red ball 10 times out of 30 times from a bag that contains red and black balls, then the probability of picking a black ball is:

• A. $\frac{1}{4}$
• B. $\frac{1}{3}$
• C. $\frac{2}{3}$
• D. $\frac{1}{2}$

Answer 1

The correct option is C $\frac{2}{3}$

We know, probability of an event E is given by,
$P\left(E\right)=\frac{Numberoftrialswheretheeventhappened}{Totalnumberoftrials}$

Probability of picking a red ball
$=\frac{10}{30}=\frac{1}{3}$

We know that the sum of probabilities of all possible outcomes of an event is 1.
Hence, the probability of picking a black ball
= 1- (Probability of picking a red ball)
= $1-\frac{1}{3}$
= $\frac{2}{3}$