Question

Terri has 7 pens in a box.

2 of the pens are blue.
4 of the pens are red.

Terri takes at random a pen from the box and writes down it's colour. Terri puts the pen back in the box.
Then Terri takes at random a second pen from the box and writes down it's colour.

a) complete a probability tree diagram.

b) work out the probability that Terri takes exactly one pen of each colour from the box.

Answer 1

a) I have attached an image of a probability tree diagram.

b) 0.02332 (please round to where you need)

The probability that Terri chooses a blue pen is 2/7. The probability that Terri chooses a red pen is 4/7. The probability that Terri chooses neither a red nor blue pen is 1/7.

2/7 x 4/7 x 1/7 = 0.02332

Hope this helps! :)