Question

A box contains 16 black and 14 white balls.if a ball is taken from it,what is the probability of it not being black?
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Answer 1

Answer:

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Sample space (total number of balls) = 7 + 14 = 21;

Pr (Selecting a first black ball) = Number of black balls / Sample space

= 14 / 21;

and since selection is done without replacement (i.e. the selected ball is not returned to the box but kept somewhere else), the number of black balls reduces by one, making the number of black balls left to be 13 and the total number of balls left (New sample space) = 20;

Pr (Selecting a second black ball) = 13 / 20;

and since events are independent, (i.e. the outcome of the first does not dictate the outcome of the second), you multiply the respective probabilities.

Hence,

Pr (Selecting two black balls) = Pr ( Selecting a first black ball) * Pr (Selecting a second black ball)

= (14/ 21) *(13/ 20);

= 13/30

Answer 2

0.47 is the answer

Probability of not black ball=P(A)

Total outcome=16+14=30