know the probability of being in your  is about we'll now find out ( )which just represents the overall probability of buying something irrespective of your age gmpbu upubm vsdibtft qsjou  vsdibtf  vsdibtf that works out to bein this exampleabout can just take the total number of things purchased by everybody regardless of age and divide it by the total number of people to get the overall probability of purchase alrightso what do have herei have the probability of purchasing something given that you're in your being about %and then have the probability of purchasing something overall at about now if and were independentif age didn' matterthen would expect the ( |fto be about the same as (ei would expect the probability of buying something given that you're in your to be about the same as the overall probability of buying somethingbut they're notrightand because they're differentthat tells me that they are in fact dependentsomehow so that' little way of using conditional probability to tease out these dependencies in the data let' do some more notation stuff here if you see something like ( ) (ftogetherthat means multiply these probabilities together can just take the overall probability of purchase multiplied by the overall probability of being in your tqsjou   vsdibtf   vsdibtf that worked out to about just from the way probabilities worki know that if want to get the probability of two things happening togetherthat would be the same thing as multiplying their individual probabilities so it turns out that ( ,fhappeningis the same thing as ( ) (fqsjou    vsdibtf gmpbu qvsdibtft    vsdibtf 