math problem, pls help!

[virus]

Hey guys n gals, I seek your help again.

Im usually good with math but I hate probability problems.. Help me understand this one!!!!!!!!!!!!!!!!!!!!!!!!!!!! {PLS}

Problem: "A test consists of 10 multiple-hoice questions, each with FIVE possible answers with only one being the correct solution. To pass the test a student must get 60% or higher. If a student randomly guesses, what is the probability that the students will pass the test?"

I know I need to set-up a normal distribution then find the z-score value, but the multiple choice thing is messing me up!

Please help!

[virus]

Well my approach was off.

I think I solved the problem so NVM for the help.

[Rickster]

i used to be so good at these.....its all in the fukin wording >_<

[Caferacer]

Jebus I hate stat stuff like that.

If you have a problem based around calculus or multivariate I'm there but I hate those kinds of problems :P

[FoRuMbOaRdS360]

Its pretty easy. I forgot exactly how to do it so. heres it. You have 10 questions you need to get 6 right. So each one has a probability of 20%. So if you take the probability and multiply it by the number of getting 6 right is this

Just seems really low.

.2 * .2 *.2 * .2 * .2 * .2=

MIght be wrong.. been a few years since I did probability. If you need some integrals though :P

[virus]

Originally Posted by FoRuMbOaRdS360

Its pretty easy. I forgot exactly how to do it so. heres it. You have 10 questions you need to get 6 right. So each one has a probability of 20%. So if you take the probability and multiply it by the number of getting 6 right is this

Just seems really low.

.2 * .2 *.2 * .2 * .2 * .2=

MIght be wrong.. been a few years since I did probability. If you need some integrals though :P

Close, the approach I took was I determined I needed to get 6 answers correct (like you said.) The probability of SUCCESS was as u stated, .20 and the probability of failure was .80.

I used this formula for determining the probability of events with a binomial outcome: p(r) = nCr * p^r * q^(n-r)

I did this for every possible answer correct above 6 (seeing u could get 6, 7, 8, 9 or all answers to pass the test.)

I added the probabilities and got around a .64% chance of passing. This seems high, but im almost 100% sure this is how to solve the problem.



Correct me if I am wrong anyone.

[FoRuMbOaRdS360]

64 does seem really high and thats a really weird formula. But it sounds better than my answer. I know Im doing it the right way just seems like i missed a step or somthing. Like I said its been awhile for me.

[virus]

Well, when I multiply .2 x 6 I get 1.2 and the percent can't be above 100.

The formula I used can be broken down into this:

p(r) = nCr * p^r * q^(n-r)
...( ^ means 'raised' to the whatever power)

r = the number of events involved ( here I did p(6),p(7) ...p(10) )
nCr = combinations of n, taken r at a time; or how many ways can we end up with r events in n trials
nCr = n! / r!(n-r)!
p = probability of success
q = probability of failure

I got a nifty feature on my calculator that did the nCr part quick for me, i didnt have to use the n!/r!(n-r)! formula everytime.

I don't know, we'll see tomorrow I guess cause im going to bed. I'll let everyone what the scoop is (if they even care.

[Papasmurf]

You must have done it wrong. If theres only a 20% chance to get one question right, theres no way theres a 64% chance to get more than half of them right. Im too tired to work this out, and i suck at probability, but your approach seems wrong.

[Lifter101]

It's supposed to be .2 to the power of 6 not times 6.

[FoRuMbOaRdS360]

Originally Posted by Lifter101

It's supposed to be .2 to the power of 6 not times 6.

Thats what I put but it seems super low.

[wnxmaximus]

I think its pretty simple to do.

.2/6 = .0333333

%3.333 of passing.

That is what seemed to make sense to me, but maybe not, i guess we will see when you post the correct answer, be sure to do so.

[NiteHawk]

That was my toughest subject. I could barely pass Algebra, so once I satisfied my math requirement for school, I never took anymore.

[virus]

My answer was .0063... rounded up was .0064, for some reason I was thinking that it meant 64 percent, DUH its .64 percent of success.


.64% of success is more do-able and that is the answer, confirmed by the teacher and all. For those who care.


My approach was right too n there are other ways and formulas to solve the problem.


Thanks for everyones input tho. I HATE PROBABILITY!

[Traps]

.2 the the 6th power is 0.000064 which is .0064% ?!?!?

[virus]

Maybes hes right with his approach. I know theres other ways of solving this.

[gymNut]

You pass if you get 6, 7, 8, 9, or 10 right.
prob of 6 right = 0.2 ^ 6 = 0.000064
prob of 7 right = 0.2 ^ 7 = 0.0000128
prob of 8 right = 0.2 ^ 8 = 0.00000256
prob of 9 right = 0.2 ^ 9 = 0.000000512
prob of 10 right = 0.2 ^ 10 = 0.0000001024
Add them up, you get the total probability of passing.
I get 0.00799%

[theara]

i was hoping the question would have been one on calculus/physics stuff. I suck at stats, well i don't care for it.

[Hannainnc]

you guys are so smart

[Noir]

You only need a 50% to pass anyway