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

The probability of drawing a red or a white marble is
`P(red \:or\: white) =(2)/(3)`.

Explanation:

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

`P(E)=(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)=(3)/(12)+(5)/(12) =(8)/(12) =(2)/(3)`