Friday, November 17, 2006

A Bit of Maths...

There are 30 objective questions in an Economics examination paper.

Let X be the number of questions that I scored correct in the paper.
Therefore X~N(30, 0.25)

0.25 is the probability that I will get a question correct.
0.75 is the probability that I will get a question wrong.

If I magically manage to get every single question correct, the probability for that event occuring will be...
P(X=30) = 30C30 (0.25)30 (0.75)0 = 0.00000000000000000086736

Let's say that I know only half of the paper. So, I estimate that I'll get 15 questions correct...
P(X=15) = 30C15 (0.25)15 (0.75)15 = 0.000000000012445

Then let's say that the gods frown on me, and I shockingly end up with not even a single question correct...
P(X=0) = 30C0 (0.25)0 (0.75)30 = 0.00017858

Hence, the probability of me having no questions correct is definitely higher than me mysteriously scoring all questions correct by random choosing.

I'm so doomed in my Economics.

4 comments:

ks said...

No. U would be doom not only for economics but for all the other objective papers if u use probability this way...

__earth said...

given that you actually know how to use your statistics, I bet you'd do fine.

Glassy said...

"A bit"?! A BIT?!

*salutes you* Fellow Math nerd! Hahaha.

Hanedin said...

Really liked your blog...