# Odds - Quant Methods

This is one of those small areas which should be absolutely fine but I get questions wrong on.

If you have say 52 card deck and you want to know the odds against picking up a spade. What is it?

13/52 cards are spades = 0.25

Isnt the odds formula = P = Probability of spade / (1- probability of spade) = 0.333

Are odds against the reciprocal of this? 1-p / p = 0.75/ 0.25 = 3???

A) 3:1

B) 1:3

C) 4:1

I said B 1:3 because but answer is 3 to 1.

Can someonw calrify?

Thanks

Because you are asked of odds against smth. Then odds are P of not happening : P happening. If you were asked of odds of picking up a spade then your answer would be correct.

Maybe remember these two formuals, as if there aren’t enough to know already, ha… Plug in the values for the below, hopefully this helps

odds against event (1-P(E)) / P(E)

odds for event P(E)/ (1-(P(E))

If you think about sports betting – the Belmont Stakes are being run a week from Saturday, not that anyone on _ this _ forum will care – they always quote the odds against a particular horse, driver, team, whatever winning, and they’re generally greater than 1:1. So the odds against getting a spade are 39:13 (39 non-spades versus 13 spades) or 3:1; the odds in favor of getting a spade are 13:39 or 1:3.