Question

A jar contains 3 red, 4 blue, and 5 white marbles. The probability of drawing a red or a white marble is 2/3.

Answer 1

add 5 + 3 together to = 8. since altogether it equal's 12. The answer would be 8/12 -> simplified to 2/3. 
your answer is correct

Answer 2

Answer:

The probability of drawing a red or a white marble is $P(red \:or\: white) =\frac{2}{3}$.

Step-by-step explanation:

The probability of the happening of an event $E$, denoted by $P(E)$, is defined as

                                   $P(E)=\frac{Number \:of\:favourable \:outcomes }{Total \:number \:of \:possible \:outcomes}$

If events A and B are mutually exclusive, then the probability of A or B is simply:

                                         $P(A \:or\: B)=P(A)+P(B)$

Two events are mutually exclusive if it is not possible for both of them to occur.

We have the event $E=red \:or \:white$ and we know that the jar contains 3 red, 4 blue, and 5 white marbles.

So,

The total number of possible outcomes is 12, this is the total number of marbles in a jar.

And the probability of drawing a red or a white marble is

                 $P(red \:or\: white)=P(red)+P(white)=\frac{3}{12}+\frac{5}{12} =\frac{8}{12} =\frac{2}{3}$