maths homework?

[pennychoo]

wasnt sure what topic to place this question so i settled for this one.
On the basis that i am crap at maths and my daughter is badgering me for a little help with the old homework?
Not asking for you to do it for me just need a clue as to how to reach the answer:
Q: THERE ARE 2 RED AND 8 BLUE BALLS IN A BAG. HOW MANY REDS DO YOU EXPECT IN 30 TRIALS?

Q: THERE ARE " " " " " " " " HOW MANY REDS DO YOU EXPECT IN 15 TRIALS?
THANKS X
ps IT HAS TO BE IN FOR TOMORROW lol

[janetsflower]

well thats ten balls in total and 3 x 10 = 30 so i would say 3 x 2 = 6 red balls and 3 x 8 = 24 blue balls in 30 trails. then do one and half times for the 15 trials so 3 red and 12 blue. But that might be too simple because i am crap at maths too. How old is your daughter? Is it aimed at someone whose maths level i might attain ie below 10 years or if shes over that then i probably got it wrong!!

[janetsflower]

hey, you must let me know what the right answer is when she hands it in

[pennychoo]

Hey Janet thank you so much for attempting, im still none the wiser, but i will let you know how you did at school, and if you get detention i will be sure to let you know!!! lol

[janetsflower]

Lol!! You can't get detention for trying only if you don't hand anything in!! Its my best effort, i hope its right

[butterfly2]

i wouldnt worry about it your daughter will have to ask her teacher about it if she and you cant figure it out. Im sure they will be glad to go thorught it with her. x

[Buenchico]

Janetsflower has got the answers right but, since you still seem unable to explain it to your daughter, I'll have a go:

Q1: 2 out of 10 balls are red, so the probability of getting a red ball is 2/10. (That's 2 over 10, or two tenths. Writing fractions on AB is tricky!).

So you expect to get a red ball on two tenths of the occasions on which you select a ball from the bag. Since this is done 30 times, the expected number of red balls is two tenths of 30, and 2/10 x 30 = 6.

Q2. Everything is the same as before, except that a ball is only drawn out on only 15 occasions, so the sum becomes 2/10 x 15 =3.

NB: I strongly recommend that you check that you've read the questions correctly. It's rather unusual for a book (or a teacher) to effectively ask the same question twice (i.e. only the number of trials has changed). It would be more likely that, if the first question asks about the expected number of red balls, the second question would ask about the expected number of blue balls. (If you want blue balls, instead of red ones, just multiply by 8/10 instead of 2/10).

Chris

PS: It sounds like those questions were set by an inexperienced teacher. During 15 years of teaching maths, I learnt to talk about putting counters into a bag, never balls. Otherwise, sooner or later, you find yourself asking your class something like "What is the probability that I've got two blue balls? That is absolutely guaranteed to start any class giggling and it's almost certain that some wag will shout out "Doesn't that depend upon how cold it is, sir?" ;-)

[kwicky]

As Chris says treat the numbers as fractions:

Total no of balls = 10
Red balls =2 therefore 2/10 which = 1/5
Blue balls =8 therefore 8/10 which = 4/5

Q1. Number of trials =30

Therefore 30 x 1/5(above) = 6 reds
=====================

Q2. Number of trials=15
which is half the previous answer
which is 3 reds
============

[pennychoo]

Cheers and thanks to EVERYBODY who helped, and your right, it was the colour of the 'balls' that differentiated the questions, - although like you say it should possibly have said 'counters' it was definately 'balls' that was used, however the chances of having 2 blue ones are nil, as she's a woman! Unless of course.....................nah, lets not go there lol x

[pennychoo]

Just to let everyone know, you all got 10/10 in the maths homework, and deserve a big pat on the back xx
and thank you once again. : )