Question

Jenna has a bag that contains 7 red marbles and 25 blue marbles. She selects a marble at random, and then, without replacing the first one, selects another marble at random.

What is the probability that Jenna selects a blue marble and then a red marble? Round your answer to the nearest percent.

P(blue and red) ≈ %

Answer 1

@tkhunny

Answer 2

Didn't we already do this one? You're still not showing your work.

Total Marbles = 32

p(blue marble on first draw) = What / 32?

Answer 3

0.78?

Answer 4

@tkhunny is 0.78 right?

Answer 5

@hysusonic

Answer 6

Well, I was hoping for 25/32. It's more instructive than 0.78125

Okay, we pull out one blue ball.

What is p(red ball on second draw) = What/31?

Answer 7

7/32=0.21

Answer 8

Nope. We took out a blue ball. Try again.

Answer 9

7/31?

Answer 10

Perfect.

So, what is the probability of BOTH of those events?

p(blue then red) = p(blue on 1st)*p(red on second) = What?

Answer 11

i don't understand

Answer 12

It's just substitution problem at this point.

p(blue then red) = p(blue on 1st)*p(red on second) = \(\dfrac{25}{32}\cdot\dfrac{7}{31}\)

That's all there is to it.

Answer 13

i got 175/992

Answer 14

17.6?

Answer 15

There it is. The fractions are just for learning what is going on.

17.6% or 0.176