Math CentralQuandaries & Queries


Question from Patrick, a student:

My question involves a video game called Guild Wars.  In the game you can have modifications (mods) on items.  One such mod is that you have a 20% chance to halve the casting time of a spell. You can have 2 of these mods available to you.  Now, it is to my understaning that combined, you would have a 32% chance to halve the casting time and a 4% chance to quarter the casting time.  Is this correct?

Hi Patrick.

When dealing with probabilities, you multiply independent choices together. For example, the probability of drawing a heart from a full deck of cards is 25%. If I draw a card from each of two full decks, the probability that both are hearts is 25% x 25% = 6.25%.

One technique we can use is a probability tree. Here is one fitting your description:

So your calculations are correct.

Stephen La Rocque. >

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