Probability of Divisibility

Date: 06/18/2002 at 19:19:18
From: Lisa Vinson
Subject: common fractions

What is the probability that a randomly selected three-digit number 
is divisible by 5? Express your answer as a common fraction?

Date: 06/18/2002 at 20:45:19
From: Doctor Ian
Subject: Re: common fractions

Hi Lisa,

How many 3-digit numbers are there?  Call that Q.  (If you're not 
sure how many there are, think about how many miles you could drive 
when the odometer in your car reads between 100 and 999.) 

How many of them are divisible by 5?  Call that P.  (If you're not 
sure how many there are, start listing them.  You should quickly see 
a pattern.)

Once you've found P and Q, the probability you're looking for is 
P/Q. 

Does this help? 

- Doctor Ian, The Math Forum
  http://mathforum.org/dr.math/