Biology Forums - Study Force

At the end of a mathematics examination, a candidate has five question left to complete; two are on statistics;two are on trigonometry and the other is on algebra.

If the questions were completed in random order, what is the probability that both statistics questions would be completed before either trigonometry questions?

not just getting you to do homework, would really appreciate  someone explaining how to do it :)

well you do all of them times together
then you minus sxs probability
then it will be those first i think

you work out the probability of all the events happening that would fulfill what they are asking, so either the person would do the two statistics questions first or the person would do the algebra then the two statistics or the person would do one statistic then one algebra then one statistic. you have to count all these events twice because there are two statistics questions so he could do the first one first or the second one first each time.
the probability of one event happening after another is the probability of each event times by each other.
the probability of a set of events happening or another set of events happening is the probability of one set of events added to the probability of the other set of events.
so the probability of doing stats then stats is 2/5 * 1/4 (you change the probability because you cant do the same question twice)
the probability of doing stats algebra stats is 2/5 * 1/4 *1/3
the probability of doing algebra then both stats is 1/5 * 2/4 * 1/3
so then add them all up (remember you have to count each one twice because he could do the first stats question first then the second second or the first second and the second first)
so you have
2*(2/5 * 1/4) + 2*(2/5 * 1/4 * 1/3) + 2*(1/5 * 2/4 * 1/3) which equals 1/3
i hope that was clear and helpful

S = statistics, T = trig, x = places where algebra can be placed

x S x S x T x T x

favorable ways = 5c1 (agebra) * 2! *2! = 20
total ways = 5!= 120
Pr = 1/6 <-----------

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