probability

 

Andy spins a fair spinner numbered 1 - 5 and rolls a fair dice.     
What is the probability of spinning a multiple of 4 and rolling a factor of 15?     

 

Between 1 & 5 inclusive, the only multiple of 4 is 4 itself.     

So, there is one chance out of five of landing on it.     

This probability is 1 / 5     

 

Between 1 & 6 inclusive, the factors of 15 are 1, 3, and 5.     

So, there are three chances out of six of landing on one of them.     

This probability is 3 / 6.     

 

For the probability of both things happening at the same time,     

multiply the probabilities together.     (1 / 5) • (3 / 6) = 3 / 30  =  1 / 10     

 

Take notice that I distinguished between a multiple and a factor.     

They are are not the same thing.     

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