Question

Sue has 20 biscuits There are: 12 plain biscuits 5 chocolate biscuits 3 currant biscuits Sue takes two random biscuits Work out the probability that the two biscuits were not the same type

Answer 1

58.43%

Explanation:

The first thing we must do is calculate the probability of when both are equal, that is, take out two cookies of the same type, since we can calculate that they are not equal by means of their complement:

The probability that they are equal is:

P (plain, plain) = (12/20) (11/19)

= 132/380

P (chocolate, chocolate) = (5/20) (4/19)

= 20/380

P (currant, currant) = (3/20) (2/19)

= 6/380

The final probability would be the sum of these:

P (equal) = 132/380 + 20/380 + 6/380

P (equal) = 158/380

P (equal) = 0.4157

The probability that they are different is the opposite of the probability that they are equal, that is, the complement. Therefore, the probability that they are different is:

P (different) = 1 - 0.4157

P (different) = 0.5843

In other words, the probability would be 58.43%