Which Person (if any) has a greater chance of picking out the Red ball?

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In summary, Person A has a higher chance of picking out a Red ball because they get two attempts, giving them a probability of 2/5 compared to Person B's probability of 1/4 with one attempt. This can be proven using the complement rule or by directly looking at the different scenarios. Therefore, it can be concluded that having two attempts rather than one increases the chances of picking out a Red ball.
  • #1
pwange
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A)
There are 5 balls inside bag A. They're all a different color (Red, Blue, Green, Orange, Purple).

Person A has two attempts to pick a Red ball from inside bag A:

1st Attempt: 1/5 chance = 20% = Let's say Person A picked out a blue ball.

2nd Attempt: 1/4 chance = 25%.

B)
There are 4 balls inside bag B. They're all a different color (Red, Green, Orange, Purple).

Person B have one attempt to pick a Red ball from inside bag B:

1st Attempt: 1/4 chance = 25%.

Question:
Which Person (if any) has a greater chance of picking out a Red ball?

My Answer:
Person A has a higher chance, because they get two attempts. Although I have no clue how to prove that.
Nor do I know by how much.

The answer might be equal (25% on both), but that doesn't make much sense to me.
I'd rather have two attempts than one.

Help please...
 
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  • #2
For person A, we can approach this directly:

We look at the case where red was drawn first, OR red was not drawn first but is drawn second.

\(\displaystyle P(\text{Red})=P(\text{First draw red})+P(\text{First not red AND second red})\)

\(\displaystyle P(\text{Red})=\frac{1}{5}+\frac{4}{5}\cdot\frac{1}{4}=\frac{2}{5}\)

We can also use the complement rule:

We know it is certain the person A will draw red in the first two draws, OR will not draw red in the first two draws:

\(\displaystyle P(\text{Red})+P(\text{Not red})=1\)

\(\displaystyle P(\text{Red})=1-P(\text{Not red})\)

\(\displaystyle P(\text{Red})=1-\frac{4}{5}\cdot\frac{3}{4}=1-\frac{3}{5}=\frac{2}{5}\)

So, we see for person A we have:

\(\displaystyle P_A(\text{Red})=\frac{2}{5}\)

And it is easy to see that for person B we have:

\(\displaystyle P_B(\text{Red})=\frac{1}{4}\)

Now, we know:

\(\displaystyle 8>5\)

Divide through by 20:

\(\displaystyle \frac{2}{5}>\frac{1}{4}\)

Hence:

\(\displaystyle P_A(\text{Red})>P_B(\text{Red})\)
 

FAQ: Which Person (if any) has a greater chance of picking out the Red ball?

What factors affect a person's chance of picking out the Red ball?

The main factors that affect a person's chance of picking out the Red ball are the total number of balls in the selection, the number of Red balls in the selection, and whether the selection is done with or without replacement.

Does the order in which the balls are picked affect a person's chance of picking out the Red ball?

No, the order in which the balls are picked does not affect a person's chance of picking out the Red ball. Each ball has an equal chance of being picked regardless of the order.

If there are more Red balls in the selection, does a person have a greater chance of picking out the Red ball?

Yes, if there are more Red balls in the selection, a person has a greater chance of picking out the Red ball. This is because there are more Red balls to choose from, increasing the likelihood of selecting one.

Does the number of players affect a person's chance of picking out the Red ball?

Yes, the number of players can affect a person's chance of picking out the Red ball. If the selection is done with replacement, each player's chance remains the same regardless of the number of players. However, if the selection is done without replacement, the number of players can decrease the chance of picking out the Red ball as more players make selections before them.

Can a person's strategy or method of picking balls affect their chance of picking out the Red ball?

No, a person's strategy or method of picking balls does not affect their chance of picking out the Red ball as long as the selection is done randomly. Each ball has an equal chance of being picked regardless of the method used.

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