You are Here: Home >< Maths

# s1 help, Discrete random variables. Watch

1. A game is made in which you have to hit a moving target, with an air rifle.
a player has up to 3 pellets in a round. 5 points are scored if a target is hit, but the round is over if missed.

J has a constant probability of 0.4 of hitting the target.

X is the random variable, no. of point scored in a round.

a.find the probability that J gets 15 points in a round. I got 0.064
b.find the probability distribution of x. when x=0. i got 0.6
x=5, 0.24
x=10, 0.096
x= 15, 0.064
A game consists of 2 rounds.

c. find the probability that J scores more on the 2 round that the first.

I have no idea on how to answer c, any help is appreciated. Thanks
2. (Original post by Hi, How are you ?)
A game is made in which you have to hit a moving target, with an air rifle.
a player has up to 3 pellets in a round. 5 points are scored if a target is hit, but the round is over if missed.

J has a constant probability of 0.4 of hitting the target.

X is the random variable, no. of point scored in a round.

a.find the probability that J gets 15 points in a round. I got 0.064
b.find the probability distribution of x. when x=0. i got 0.6
x=5, 0.24
x=10, 0.096
x= 15, 0.064
A game consists of 2 rounds.

c. find the probability that J scores more on the 2 round that the first.

I have no idea on how to answer c, any help is appreciated. Thanks
Here is a start

Scores 5 in first round and then more in the next round = 0.24 x (0.096+0.064)

Does that help
3. (Original post by TenOfThem)
Here is a start

Scores 5 in first round and then more in the next round = 0.24 x (0.096+0.064)

Does that help
I see that in the first round, if you only score 5 points, that a probability of 0.24, but I don't see why you multiplied by (0.096+0.064)
4. (Original post by Hi, How are you ?)
I see that in the first round, if you only score 5 points, that a probability of 0.24, but I don't see why you multiplied by (0.096+0.064)
Because you want him to score more than 5 in the second round
5. (Original post by TenOfThem)
Because you want him to score more than 5 in the second round
so to get more that 5, you add the probabilities of 10 and 15, as they are higher and so the probabilities are (0.096+0.064), then you times them.

Ok, what should i do next?
6. (Original post by Hi, How are you ?)
so to get more that 5, you add the probabilities of 10 and 15, as they are higher and so the probabilities are (0.096+0.064), the you times them.

Ok, what should i do next?
Consider the other options (other than 5 in the first round)
7. (Original post by TenOfThem)
Consider the other options (other than 5 in the first round)
could score 10 in first round, then 15 in next so, 0.096 x 0.064, right?

and those are the only options left?
8. (Original post by Hi, How are you ?)
could score 10 in first round, then 15 in next so, 0.096 x 0.064, right?

and those are the only options left?
Is there nothing else that you can score in round one?
9. (Original post by TenOfThem)
Is there nothing else that you can score in round one?
Oh yeah, the 0, so its 0.6 X (0.096 + 0.064 + 0.24)
10. (Original post by Hi, How are you ?)
Oh yeah, the 0, so its 0.6 X (0.096 + 0.064 + 0.24)
indeed
11. (Original post by TenOfThem)
indeed
What shall I do next?
12. (Original post by Hi, How are you ?)
What shall I do next?
seriously?

you have some viable options, what would you usually do with the probabilities to get the total probability
13. (Original post by TenOfThem)
seriously?

you have some viable options, what would you usually do with the probabilities to get the total probability
14. (Original post by Hi, How are you ?)
yes
15. (Original post by TenOfThem)
yes
I see, 1 more q, why do you add them?
16. (Original post by Hi, How are you ?)
I see, 1 more q, why do you add them?
Why wouldn't you

This is GCSE maths
P(A and B) = P(A) x P(B)
P(A or B) = P(A) + P(B) (if mutually exclusive)

Imagine a tree diagram

First branches are the score for round 1
Second branches are More or Not

You have multiplied along the branches to get (0, more) and (5, more) etc

17. (Original post by TenOfThem)
Why wouldn't you

This is GCSE maths
P(A and B) = P(A) x P(B)
P(A or B) = P(A) + P(B) (if mutually exclusive)
I see, makes sense. Thanks
18. (Original post by Hi, How are you ?)
I see, makes sense. Thanks
Did you see my edit

x

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: April 11, 2013
Today on TSR

### Should I ask for his number?

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE