Browse · MATH
Printjmc
counting and probability senior
Problem
How many positive integers less than or equal to 100 have a prime factor that is greater than 4?
Solution
The easiest solution is to find the number of positive integers with only 2 and 3 as their prime factors. If the number has no factors of 3, the qualifying numbers are for 7 total. If there is one factor of 3, we have for 6 total. With two factors of 3, we have for 4 total. With three factors of 3, we have for 2 total. Finally, gives us 1 more. So, there are positive integers less than or equal to 100 that have only 2 and 3 as prime factors. Therefore, there are positive integers less than or equal to 100 that have a prime factor greater than 4.
Final answer
80