simple probability

[Dencology]

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A large basket of fruit contains 3 oranges, 2 apples and 5 bananas. If a piece of fruit is chosen at random, what is the probability of getting an orange or a banana?guys how is it that the ans is 4/5. i think it is 3/10 for orange and 1/2 for banana?


In a class of 30 students, there are 17 girls and 13 boys. Five are A students, and three of these students are girls. If a student is chosen at random, what is the probability of choosing a girl or an A student? ans is 19/30
choosing a girl is 17/40 (and when it says "or" it means that we have to add the two probabilities together so) and i don't know the rest.

 

[PooyaH]

Since it says an orange OR a banana then just add the probability of each:

3/10 + 1/2 = 8/10 = 4/5

 

[Mamona]

In a class of 30 students, there are 17 girls and 13 boys. Five are A students, and three of these students are girls. If a student is chosen at random, what is the probability of choosing a girl or an A student? ans is 19/30
choosing a girl is 17/40 (and when it says "or" it means that we have to add the two probabilities together so) and i don't know the rest.

First the probability of choosing a girl is 17/30 and probability of choosing an A student is 5 -3 (the 3 girls already used in the first part, they can't be part of both probablities.... so is not 5/30, but 2/30) Finally add both probabilities
17/30 + 2/30 = 19/30

 

[Dencology]

how did you get 2/30? from the 5 A students, three are girl and 2 are boys so 2/30 is the boys and not the girl. pls correct me ?

In a school, 14% of students take drama and computer classes, and 67% take drama class. What is the probability that a student takes computer class given that the student takes drama class?

ans. 21%. how?

 

[PooyaH]

how did you get 2/30? from the 5 A students, three are girl and 2 are boys so 2/30 is the boys and not the girl. pls correct me ?

In a school, 14% of students take drama and computer classes, and 67% take drama class. What is the probability that a student takes computer class given that the student takes drama class?

ans. 21%. how?

The question says what is the probability of choosing a girl or an A student! It says 3 of the girls are A student...So you have already counted the probability of picking a girl which is 17/30...and since there 5 A students, and 3 of the A students are girls, it leaves 2 students that are A students, thus 2/30 should be the probability of picking an A student!

lol sorry it's beena long day, hope it makes sense lol

 

[kush87]

In a school, 14% of students take drama and computer classes, and 67% take drama class. What is the probability that a student takes computer class given that the student takes drama class?

ans. 21%. how?

What is the probability that a student takes computer class given that the student takes drama class

given --> student takes drama class (the student is one of those 67%) 67% becomes the whole...instead of the 100% of school...in other words you are not concern with the other 33%
? --> student must also have a computer class (this is 14 % of the student)

he could be any one of those 14% out of the whole 67% who take dram classes to have a computer class as well


thats why the prob is 14% out of 67% (14/67) = 0.21 = 21%