Why is there not an associative property of subtraction?

What are the relative frequencies to the nearest hundredth of the columns of the two-way table? a b group 1 102 34 group 2 18 14

International calls require the use of a country code. many country codes a 3-digit numbers. country codes do not begin with a 0 or 1. there are no restrictions on the second and third digits. how many different 3-digit country codes are possible?

Ben is three times as old as samantha, who is two years older than half of michel's age. if michel is 12. how old is ben?