Heather has a bag containing 4 marbles: 1 red, 1 blue, and 2 green. She draws 1 marble out of the bag, replaces it, and then draws another marble. What is [tex]$P$[/tex] (red then blue)?

A. [tex]\frac{1}{64}[/tex]
B. [tex]\frac{1}{32}[/tex]
C. [tex]\frac{1}{2}[/tex]
D. [tex]\frac{3}{4}[/tex]



Answer :

Sure, let's solve this step-by-step.

Given:
- The bag contains 4 marbles: 1 red, 1 blue, and 2 green.
- Heather draws a marble, replaces it, and then draws another marble.

First, let's calculate the probability of drawing each marble during one draw:

1. Total number of marbles (N):
[tex]\[ N = 4 \][/tex]

2. Probability of drawing each marble:
- Red marble (P_red):
[tex]\[ \text{P(red)} = \frac{1 \text{ red marble}}{4 \text{ total marbles}} = \frac{1}{4} = 0.25 \][/tex]

- Blue marble (P_blue):
[tex]\[ \text{P(blue)} = \frac{1 \text{ blue marble}}{4 \text{ total marbles}} = \frac{1}{4} = 0.25 \][/tex]

- Green marble (P_green):
[tex]\[ \text{P(green)} = \frac{2 \text{ green marbles}}{4 \text{ total marbles}} = \frac{2}{4} = \frac{1}{2} = 0.5 \][/tex]

Next, we need to find the probability of drawing a red marble first, then a blue marble, and then a green marble in three successive draws with replacement.

Since each draw is independent and the marbles are replaced, we can multiply the probabilities of each event happening sequentially:

[tex]\[ P(\text{red then blue then green}) = P(\text{red}) \times P(\text{blue}) \times P(\text{green}) \][/tex]

3. Calculating the combined probability:
[tex]\[ P(\text{red then blue then green}) = (\frac{1}{4}) \times (\frac{1}{4}) \times (\frac{1}{2}) \][/tex]
[tex]\[ P(\text{red then blue then green}) = 0.25 \times 0.25 \times 0.5 \][/tex]
[tex]\[ P(\text{red then blue then green}) = 0.03125 \][/tex]

Finally, express the combined probability as a fraction:
[tex]\[ 0.03125 = \frac{1}{32} \][/tex]

So, the probability [tex]\( P \)[/tex] of drawing a red marble first, then a blue marble, and then a green marble is:
[tex]\[ \frac{1}{32} \][/tex]

Therefore, the correct answer is:

[tex]\[ \boxed{\frac{1}{32}} \][/tex]