maths probability solution please

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idl
Posts: 16
Joined: Mon Oct 03, 2016 8:41 am

Re: maths probability solution please

Post by idl »

similar question that is eating my brains...
A farmer has 100 sheep in a field. 60% of the sheep are ewes, and the rest are rams. 80% of the sheep are lambs and the rest are mature sheep. 75% of the sheep are white and rest are black.
How many sheep in the field are likely to be black, mature rams?


I really need to know how to work these out. Poor kids how can they do this?
Please help me.
Guest55
Posts: 16254
Joined: Mon Feb 12, 2007 2:21 pm

Re: maths probability solution please

Post by Guest55 »

idl wrote:A farmer has 100 sheep in a field. 60% of the sheep are ewes, and the rest are rams. 80% of the sheep are lambs and the rest are mature sheep. 75% of the sheep are white and rest are black.
How many sheep in the field are likely to be black, mature rams?
100 sheep
25% are black ie 25
20% are mature ie 1/5 of 25 = 5
40% are rams 5 x 0.4 = 2

I would go in steps like this but you should get a whole number answer!
solimum
Posts: 1420
Joined: Wed May 09, 2007 3:09 pm
Location: Solihull, West Midlands

Re: maths probability solution please

Post by solimum »

But both questions are (it seems) implicitly assuming the independence of the different factors, which is by no means certain. For example, in the first case, if the favourite author writes only non-fiction (Bill Bryson maybe!) then all 20 of them could be paperbacks, or none of them. Badly worded (putting on my statistical hat) . But if the favourite author writes fiction, the answer must be zero anyway. More information needed!
idl
Posts: 16
Joined: Mon Oct 03, 2016 8:41 am

Re: maths probability solution please

Post by idl »

Yes..for the sheep question, answer is 2 :shock:
Guest55
Posts: 16254
Joined: Mon Feb 12, 2007 2:21 pm

Re: maths probability solution please

Post by Guest55 »

Yep exactly, very poor question ... at least the sheep one is clearer.
Guest55
Posts: 16254
Joined: Mon Feb 12, 2007 2:21 pm

Re: maths probability solution please

Post by Guest55 »

idl wrote:Yes..for the sheep question, answer is 2 :shock:
I see no problem with this one ...
idl
Posts: 16
Joined: Mon Oct 03, 2016 8:41 am

Re: maths probability solution please

Post by idl »

I missed the fact to work it from back every step
ToadMum
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Location: Essex

Re: maths probability solution please

Post by ToadMum »

Guest55 wrote:Yep exactly, very poor question ... at least the sheep one is clearer.
And doesn't involve the candidate indulging in the unlicensed slaughter of farm animals in the middle of the exam :lol: .
Outside of a dog, a book is a man's best friend. Inside of a dog it's too dark to read.Groucho Marx
Guest55
Posts: 16254
Joined: Mon Feb 12, 2007 2:21 pm

Re: maths probability solution please

Post by Guest55 »

Yes, take each statement in turn but this only works if the attributes are independent so that's why the book one is flawed.
idl
Posts: 16
Joined: Mon Oct 03, 2016 8:41 am

Re: maths probability solution please

Post by idl »

Toadmum: thanks for bringing smile on my face, i was in a great head rush/spin etc

Thanks to Guest55 for prompt responses.

Thanks all, i think i got hang of these now
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