Question

A bag contains 3 red marbles and 4 blue marbles.

A marble is taken at random from the bag and replaced.
Another marble is taken from the bag.
Work out the probability the the two marbles taken from the bag are the same colour.
Give your answer as a fraction.

Answer 1

25/49

Explanation:

Look: type this into your calculator EXACTLY AS IT IS HERE (3/7*3/7)+(4/7*4/7).

And you should get 25/49.

If this is a non-calculator question, do this:

(a) 3/7 * 3/7 = 9/49 (multiply numerator by numerator and denominator by denominator, or basically 3x3 = 9 and 7x7 = 49).

(b) 4/7 * 4/7 = 16/49 (multiply numerator by numerator and denominator by denominator, or basically 4x4 = 16 and 7x7 = 49).

(c) And then do 9/49 + 16/49 = 25/49.