A two-digit number is written down at random.Find the probability that the number will be
A)Smaller than 20
B)Even
C)Multiple of 5
How to solve this question ?
If it is lower than 20 you know that it is either 19, 18, 17, 16.....
If it is even it is 2, 4, 6, 8, 10, 12, 14, 16, 18 and 20.
Multiples of five lower than 20 that are even, well there is only 1: 10
If it is lower than 20 you know that it is either 19, 18, 17, 16.....
If it is even it is 2, 4, 6, 8, 10, 12, 14, 16, 18 and 20.
Multiples of five lower than 20 that are even, well there is only 1: 10
You appear to be assuming that these are "cumulative"- that is, that the "B) even" means "even and less than 20" and that "C) a multiple of 5" means "a multiple of 5 and even and less than 20". I don't believe those assumptions are warrented.
Last edited by HallsofIvy; Jan 24th 2011 at 02:03 PM.
A two-digit number is written down at random.Find the probability that the number will be
A)Smaller than 20
B)Even
C)Multiple of 5
How to solve this question ?
The obvious but blunt approach is to count all the two digit numbers that satisfy each condition and then divide by the total number of two digit numbers.