You are Here: Home >< Maths

# Probability Question Watch

1. I have been struggling with this probability question for a while now. I really have no idea where to go. Any help you can give me would really be appreciated. I have answered (a) and (b) but the rest of it has me stumped.

The answer to part a is 0.064 and b is 0.216.

A man with eczema has a 0.4 chance of suffering symptoms on a given day. In a three-day period, what is the chance of him experiencing symptoms on:

(a) 3 days
(b) none of the days
(c) exactly 2 days
(d) at least one day
(e) the final day
(a) 0.064
(b) 0.216
(c) 0.288
(d) 0.784
(e) 0.144
2. Are you familiar with binomial distribution? I was able to get an answer to C by using it. I haven't attempted the others yet.

C:
Spoiler:
Show
X~B(3,0.4)
P(x=2)
3C2 x (0.4)2 x (0.6)1 = 0.288

D:
Spoiler:
Show
X~B(3,0.4)
P(x=0)
3C0 x (0.4)0 x (0.6)3 = 0.216

1 - 0.216 = 0.784

E:
Spoiler:
Show
0.62 x 0.4 = 0.144

EDIT: There's my working out above. Try and have a go at learning binomial distribution and then tackling the questions above, before looking at how I did it.

P.S

If you're not very good at S1, believe me, you aren't the only one. I'm finding it difficult.
3. Part e follows a geometric distribution to be more precise
4. (Original post by Arg)
...
As has been said this is binomial distribution

If you are unsure of the formulae try to think through the questions

Exactly 2 days could be

YYN
YNY
NYY

The P(YYN) = 0.4 x 0.4 x 0.6

The other probabilities are the same

For at least one day, you just need to consider NNN and take this away from 1 ... can you see why?

I am afraid that I disagree with the answer for (e) if that is the actual question
5. Agree with TenOfThem.

The answer to (e) is incorrect if that's the question exactly as worded.

If (e) was "the final day only", then the given answer would be correct.
6. (Original post by TenOfThem)
The P(YYN) = 0.4 x 0.4 x 0.6

The other probabilities are the same
I have never heard of binomial distribution before.
Also 0.4 x 0.4 x 0.6 = 0.096

(Original post by TenOfThem)
For at least one day, you just need to consider NNN and take this away from 1 ... can you see why?
No.

(Original post by TenOfThem)
I am afraid that I disagree with the answer for (e) if that is the actual question
(Original post by ghostwalker)
Agree with TenOfThem.

The answer to (e) is incorrect if that's the question exactly as worded.

If (e) was "the final day only", then the given answer would be correct.

That is the actual question and actual answer. I suppose it is possible that my sheet is wrong.
7. (Original post by Arg)
I have never heard of binomial distribution before.
Not sure why you are doing these question then

Also 0.4 x 0.4 x 0.6 = 0.096
Because you have not included the other options

I only showed Yes Yes No ... there are other possibilities ... for example Yes No Yes

No.
hmmmmm

You cannot see that you either have No No No or at least one day has to be Yes?

That is the actual question and actual answer. I suppose it is possible that my sheet is wrong.

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 12, 2013
Today on TSR

### Falling in love with him

But we haven't even met!

### Top study tips for over the Christmas holidays

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

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.