There is a bag filled with 3 blue and 4 red marbles. A marble is taken at random from the bag, the colour is noted and then it is not replaced. Another marble is taken at random. What is the probability of getting 2 that are different in colour?

The required probability is 4/7.

Step-by-step explanation:

The sample space for the experiment is: { BB, BR, RB, RR }

The outcome of the event we require is: { BR, RB }

The probabilities for each outcome is given as:

BB: 3/7 x 2/6 = 1/7

BR: 3/7 x 4/6 = 2/7

RB: 4/7 x 3/6 = 2/7

RR: 4/7 x 3/6 = 2/7

Adding the probabilities we have:

{ BR, RB} = 2/7 + 2/7 = 4/7

That's it!