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roadrunner98
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#1
Report Thread starter 3 years ago
#1
I've collected two questions that I'm really confused on how to do.
1. Shabeen has a biased coin. The probability that the coin will land on heads is 0.6. Shabeen is going to throw the coin 3 times. She says the probability that the coin will land on tails 3 times is less than 0.1. Is Shabeen correct?

The answer is Yes cos 0.4*0.4*0.4. Could someone pls explain how to do these questions cos I'm not sure when to multiply or add probabilities.

2. Jeff is choosing a shrub and a rose tree for his garden. At the garden centre there are 17 different types of shrubs and some rose trees. Jeff says, "There are 215 different ways to choose one shrub and one rose tree.". Could Jeff be correct?
I attempted to do one of the combination formulas mainly cos i didn't know how to solve this. If someone could explain these two questions to me I would really appreciate it
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Gent2324
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#2
Report 3 years ago
#2
(Original post by roadrunner98)
I've collected two questions that I'm really confused on how to do.
1. Shabeen has a biased coin. The probability that the coin will land on heads is 0.6. Shabeen is going to throw the coin 3 times. She says the probability that the coin will land on tails 3 times is less than 0.1. Is Shabeen correct?

The answer is Yes cos 0.4*0.4*0.4. Could someone pls explain how to do these questions cos I'm not sure when to multiply or add probabilities.

2. Jeff is choosing a shrub and a rose tree for his garden. At the garden centre there are 17 different types of shrubs and some rose trees. Jeff says, "There are 215 different ways to choose one shrub and one rose tree.". Could Jeff be correct?
I attempted to do one of the combination formulas mainly cos i didn't know how to solve this. If someone could explain these two questions to me I would really appreciate it
its 0.4 x 0.4 x 0.4 because you need the probability that it will first land on tails (0.4) and then it MUST land on tails again (0.4) and again. so it cant be 0.4 x 3 because then its a 1.2 probability which is impossible. so if you need the probability that an event will happen and then another event will happen, you times them

as for the second question, if theres 215 different combinations, then it must be 17 x (how ever many rose trees there are) so 215 / 17 = 12.647 , since its not a whole number, it must be impossible
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lydiarutharnold
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#3
Report 3 years ago
#3
(Original post by roadrunner98)
I've collected two questions that I'm really confused on how to do.
1. Shabeen has a biased coin. The probability that the coin will land on heads is 0.6. Shabeen is going to throw the coin 3 times. She says the probability that the coin will land on tails 3 times is less than 0.1. Is Shabeen correct?

The answer is Yes cos 0.4*0.4*0.4. Could someone pls explain how to do these questions cos I'm not sure when to multiply or add probabilities.

2. Jeff is choosing a shrub and a rose tree for his garden. At the garden centre there are 17 different types of shrubs and some rose trees. Jeff says, "There are 215 different ways to choose one shrub and one rose tree.". Could Jeff be correct?
I attempted to do one of the combination formulas mainly cos i didn't know how to solve this. If someone could explain these two questions to me I would really appreciate it
1
4/10*4/10 is 16/100
=4/25
4/25*4/10=16/250
16/250=0.064 so yes
Turn them into fractions- for these questions you have to multiply, not add. 0.4=4/10 or 2/5

2
Is there a specific number of rose trees?
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roadrunner98
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#4
Report Thread starter 3 years ago
#4
(Original post by Gent2324)
its 0.4 x 0.4 x 0.4 because you need the probability that it will first land on tails (0.4) and then it MUST land on tails again (0.4) and again. so it cant be 0.4 x 3 because then its a 1.2 probability which is impossible. so if you need the probability that an event will happen and then another event will happen, you times them

as for the second question, if theres 215 different combinations, then it must be 17 x (how ever many rose trees there are) so 215 / 17 = 12.647 , since its not a whole number, it must be impossible
Oh the first question makes a lot of sense now. Just to be clear the probability can never go over 1, right?
1
BTAnonymous
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#5
Report 3 years ago
#5
(Original post by roadrunner98)
Oh the first question makes a lot of sense now. Just to be clear the probability can never go over 1, right?
never
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Gent2324
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#6
Report 3 years ago
#6
(Original post by roadrunner98)
Oh the first question makes a lot of sense now. Just to be clear the probability can never go over 1, right?
yea, think of it like a % if that helps, 100% = 1 where nothing else can happen apart from that event
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roadrunner98
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#7
Report Thread starter 3 years ago
#7
(Original post by Gent2324)
its 0.4 x 0.4 x 0.4 because you need the probability that it will first land on tails (0.4) and then it MUST land on tails again (0.4) and again. so it cant be 0.4 x 3 because then its a 1.2 probability which is impossible. so if you need the probability that an event will happen and then another event will happen, you times them

as for the second question, if theres 215 different combinations, then it must be 17 x (how ever many rose trees there are) so 215 / 17 = 12.647 , since its not a whole number, it must be impossible
(Original post by lydiarutharnold)
1
4/10*4/10 is 16/100
=4/25
4/25*4/10=16/250
16/250=0.064 so yes
Turn them into fractions- for these questions you have to multiply, not add. 0.4=4/10 or 2/5

2
Is there a specific number of rose trees?
The second question doesn't really specify the number of rose trees. I just found my teachers working to this question and he found 12.6470588 and used 12 and 13. He then worked out 17*12 and 17*13 and said they are not 215
1
Gent2324
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#8
Report 3 years ago
#8
(Original post by roadrunner98)
The second question doesn't really specify the number of rose trees. I just found my teachers working to this question and he found 12.6470588 and used 12 and 13. He then worked out 17*12 and 17*13 and said they are not 215
yea the whole point of the question is that you dont know how many rose trees there are, there can only be a whole number of rose trees, so if theres 215 combinations then it must be 17 x 12.647 , there cant be 12.647 rose trees so its impossible. not to sure why your teacher did 12 and 13, you can easily prove it wrong by showing that you cant times 17 by a whole number to get 215
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roadrunner98
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#9
Report Thread starter 3 years ago
#9
(Original post by Gent2324)
yea the whole point of the question is that you dont know how many rose trees there are, there can only be a whole number of rose trees, so if theres 215 combinations then it must be 17 x 12.647 , there cant be 12.647 rose trees so its impossible. not to sure why your teacher did 12 and 13, you can easily prove it wrong by showing that you cant times 17 by a whole number to get 215
Ok this is making a lot more sense. As soon as i saw the word "combination" i thought it had something to do with permutations or combinations. Thank you for the help.
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MrCracker
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#10
Report 1 week ago
#10
what about just approximating it as 0.64 roses and shrubs in reality just means 1 roses and shrubs
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