Doreen
1
A bag contains only 8 beads

The beads are identical in all respects except colour.

3 of the beads are black and the other 5 beads are white.

A bead is taken at random from the bag and not replaced.

A second bead is then taken at random from the bag.

What is the probability that both beads are black?

i tried 3/8 + 2/7

hi

i did 3/8 * 2/7 = 3/28

what is the correct solution?

1 Like

Doreen
3
yes that is correct, but why multiply instead of add like i did, can you explain why?

because we use the probability equations

let’s say P(A)=picking a black bead during the first draw

P(B)=picking a black bead during the second draw

P(both)=P(A) * P(B/A)

in other words = P(A) * P(B knowing we picked a black bead during the first draw)

1 Like

Doreen
5
thank you so much juliette