I don't understand the explanation from the back of the book. Can someone plz explain the answers?
Thanks a bunch!
problem 432 on OG 10.
A certain junior class has 1000 students and a certain senior class has 800 students. Among these students, there are 60 siblings pairs, each consisting of 1 junior and 1 senior. If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a sibling pair?
a. 3/40,000
b. 1/3600
c. 9/2000
d. 1/60
e. 1/15
OG 10 Problem 432 on Page 134 - Probability
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- Neo2000
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IF there are 60pairs, it means there are 60students in the senior class who have a sibling in the junior class.
In order to pick 1 pair, select 1 student fm the senior class who has a sibling
This can be done in 60/800 ways
This student has only 1 sibling in the junior class and can be picked in 1/1000ways
So total number of ways = (60/800) * (1/1000)
Hope this helps
In order to pick 1 pair, select 1 student fm the senior class who has a sibling
This can be done in 60/800 ways
This student has only 1 sibling in the junior class and can be picked in 1/1000ways
So total number of ways = (60/800) * (1/1000)
Hope this helps
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The probability of an event to occur is defined as , p(E) = (number of required outcome)/(number of total outcome)
probability of two events, A and B occurring at the same time is define as p(A) and p(B)= p(A) * p(B)
now, the number of junior students, n(j) = 1000
and number of senior students, n(s) = 800
There are sixty siblings pair, each from both classes.
i.e 60 students from the junior class have one sibling each in the same class.
let p(j) be the probability of a junior student having a sibling in the senior class.
p(j) = (no. of junior students that have a sibling) / (total number of junior students)
= 60/1000 = 3/50
Also, let P(s) be the probability of a senior class student having a sibling in the junior class
therefore, p(S)= 60/800 = 3/40
Now, the probability of one junior student and one senior student being sibling
= p(J) and p(S)
= p(J) * p(S)
= (3/50) * (3/40)
= 9/2000
Hence, option C is very correct :mrgreen:
probability of two events, A and B occurring at the same time is define as p(A) and p(B)= p(A) * p(B)
now, the number of junior students, n(j) = 1000
and number of senior students, n(s) = 800
There are sixty siblings pair, each from both classes.
i.e 60 students from the junior class have one sibling each in the same class.
let p(j) be the probability of a junior student having a sibling in the senior class.
p(j) = (no. of junior students that have a sibling) / (total number of junior students)
= 60/1000 = 3/50
Also, let P(s) be the probability of a senior class student having a sibling in the junior class
therefore, p(S)= 60/800 = 3/40
Now, the probability of one junior student and one senior student being sibling
= p(J) and p(S)
= p(J) * p(S)
= (3/50) * (3/40)
= 9/2000
Hence, option C is very correct :mrgreen:
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One option is to apply probability rules.A certain junior class has 1,000 students and a certain senior class has 800 students. Among these students, there are 60 sibling pairs, each consisting of 1 junior and 1 senior. If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a sibling pair?
A) 3/40,000
B) 1/3,600
C) 9/2,000
D) 1/60
E) 1/16
So, for two siblings to be selected, 2 things must happen: we must select a junior who has a senior sibling AND the senior selected must be the sibling of the selected junior.
We get P(junior with sibling AND selected senior is sibling to selected junior)= P(junior with sibling) x P(selected senior is sibling to selected junior)
P(junior with sibling): there are 1000 juniors and 60 of them have senior siblings. So, P(junior with sibling)=60/1000
P(selected senior is sibling to selected junior): Once the junior has been selected, there is only 1 senior (out of 800 seniors) who is the sibling to the selected junior. So, P(selected senior is sibling to selected junior)= 1/800
So, the probability is (60/1000)x(1/800) = 3/40,000
The answer is A
Cheers,
Brent
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In the junior class, the probability of selecting any one sibling from the 60 sibling pairs is 60/1000. Once that person is selected, the probability of selecting his or her sibling from the senior class is 1/800; thus, the probability of a selecting a sibling pair is:weipei wrote: ↑Sat Jan 27, 2007 2:42 amI don't understand the explanation from the back of the book. Can someone plz explain the answers?
Thanks a bunch!
problem 432 on OG 10.
A certain junior class has 1000 students and a certain senior class has 800 students. Among these students, there are 60 siblings pairs, each consisting of 1 junior and 1 senior. If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a sibling pair?
a. 3/40,000
b. 1/3600
c. 9/2000
d. 1/60
e. 1/15
60/1000 x 1/800 = 3/50 x 1/800 = 3/40000
Alternatively, in the senior class, the probability of selecting any one sibling from the 60 sibling pairs is 60/800. Once that person is selected, the probability of selecting his or her sibling from the junior class is 1/1000; thus, the probability of a selecting a sibling pair is:
60/800 x 1/1000 = 3/40 x 1/1000 = 3/40000
Answer: A
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