Basic Probability (spinners,etc.)

[jonboy]

I would like you guys (and girls) to verify my answer and that my logic is correct.

We have a spinner:

Assuming each "slice" is equal: Find the odds of the outcome if the spinner is spun once.

prime or 1

1,2,3,5,7 out of 8 possible outcomes are all prime numbers and 1 is possible out of 8 choices so:

\(\displaystyle \L\bold \frac{5}{8}+\frac{1}{8}=\frac{6}{8}\to3:4\)

multiple of 4

The only mulitples of 4 I see are 4 and 2.

\(\displaystyle \L\bold \frac{2}{8}\to1:4\)

Also: A person is born in the month of September. Find the probability.

\(\displaystyle P\)(the date is the 25th)=1:30

\(\displaystyle P\)(date is before September 10)=3:10

Does this look correcto'?

 

[mcrae]

why are you counting 1 as both a prime and as 1? it should ony be 5/8 not 6/8
P=5/8 odds= 5:3

1 2 4 are multiples of 4... P=3/8 odds= 3:5

30 days in september..
P(born on 25) =1/30, odds are 1:29
P(before 10th)=9/30=3/10 odds are 3:7

 

[pka]

1 2 4 are multiples of 4... P=3/8 odds= 3:5

Good lord, do either of you know what MULTIPLE means?
There are two multiples of four: 4 & 8.

 

[jonboy]

Oh ok. Thx for the assistance and explanation. Why would you not count 1 as both as a prime and 1?

 

[mcrae]

what if the problem said "whats probability of a prime number, and a number less than 10? would you do 5/8 +8/8 =1.625? no, because that is greater than 1, which isn't possible for probability. the 1 is part of both the '1' group and the 'prime number' group, so you can't count it twice. if you counted things twice in this fashion, you would get probabilities greater than 100%...
(assuming 1 is a prime number. i odn't know)

and no i don't know what multiple means, obviously im as stupid as this poor kid who tries to help but fails

 

[pka]

Oh ok. Thx for the assistance and explanation. Why would you not count 1 as both as a prime and 1?

The number 1 is not prime!
Hence you are counting only members of {1,2,3,5,7}.

 

[jonboy]

Good lord, do either of you know what MULTIPLE means?
There are two multiples of four: 4 & 8.

I thought a multiple is whenever you can mulitply two whole numbers to get that number. 8 has no whole number that can be multiplied to get 4.

http://www.math.com/school/glossary/defs/multiple.html

A multiple of a number is the product of that number and any other whole number. Zero is a multiple of every number.

??????????

 

[pka]

??????????

My dear boy, you are in a state of total confusion.
You have the definitions of divisor and multiple inverted.

In this problem:
The divisors of 4 are 1,2 & 4.
The multiples of 4 are 4 & 8.

 

[Denis]

what if the problem said "whats probability of a prime number, and a number less than 10? would you do 5/8 +8/8 =1.625? no, because that is greater than 1, which isn't possible for probability.

mcrae, WHY "less than 10" when ONLY 1 to 8 are present :shock:
Please stop contributing to poor jonboy's confusion :twisted:

 

[JakeD]

what if the problem said "whats probability of a prime number, and a number less than 10? would you do 5/8 +8/8 =1.625? no, because that is greater than 1, which isn't possible for probability.

mcrae, WHY "less than 10" when ONLY 1 to 8 are present :shock:
Please stop contributing to poor jonboy's confusion :twisted:

Mcrae was giving an example explaining why you should not double count the probabilities when a number satisfies two conditions. M is the only one who addressed this issue and it is important because this is a probability question. It is unfortunate M and Jonboy were also tripped up by the definitions of prime and multiple. So, Denis, please show how you would explain why Jonboy was double counting probabilities in his original answer and why it is incorrect to do that. Thank you.

 

[Denis]

So, Denis, please show how you would explain why Jonboy was double counting probabilities in his original answer and why it is incorrect to do that. Thank you.

So, Jake, please show how you would explain why Jonboy was double counting probabilities in his original answer and why it is incorrect to do that. Thank you.

 

[JakeD]

So, Denis, please show how you would explain why Jonboy was double counting probabilities in his original answer and why it is incorrect to do that. Thank you.

So, Jake, please show how you would explain why Jonboy was double counting probabilities in his original answer and why it is incorrect to do that. Thank you.

No need for that. Mcrae's explanation was OK by me.