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) = ^{30}C_{30} (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) = ^{30}C_{15} (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) = ^{30}C_{0} (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.

## Friday, November 17, 2006

### A Bit of Maths...

Posted by Andy at 5:54:00 pm

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## 4 comments:

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

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

"A bit"?! A BIT?!

*salutes you* Fellow Math nerd! Hahaha.

Really liked your blog...

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