Suppose that 21 slips of paper numbered 1 to 21, inclusive, are put into a hat.
Then one slip is drawn out of the hat.
1. Find the probability that the slip with a 4 is drawn. Well let's see. We have 21 slips of paper with these numbers written on them:
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21
How many have 4 on them? I'll color any that have 4 on them red.
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21
How many did I color red? Just 1. So that's 1 out of 21.
So the probability is 1/21.
2. Find the probability that a slip with an even number on it is drawn.How many have an even number on them? I'll color any that have an even number
on them red.
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21
How many did I color red? I count 10. That's 10 out of 21.
So the probability is 10/21.
3. Find the probability that a slip with a multiple of five on it is drawn.How many have a multiple of 5
on them? I'll color any that have a multiple of 5 on them red.
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21
How many did I color red? I count 4. That's 4 out of 21.
So the probability is 4/21.
This was very easy, wasn't it?
Edwin