Answer :
Cathy and Iris have 259,459,200 ways to skip countries.
Data;
- Number of countries they are planning to visit = 9
- Number of countries they would like to visit = 13
Combination
To solve this problem, we would have to use a mathematical procedure known as combination.
Let us calculate the number of countries that would have to skip.
[tex]13 - 9 = 4[/tex]
To decide which country they have to skip, it would be 4 out of 13.
[tex]x = ^1^3C_4 = \frac{13!}{4!}[/tex]
Let's solve this
[tex]\frac{13!}{4!} = \frac{13*12*11*10*9*8*7*6*5*4*3*2*1}{4*3*2*1}\\ \frac{13!}{4!} = 13*12*11*10*9*8*7*6*5 = 259459200 ways[/tex]
Cathy and Iris have 259,459,200 ways to skip countries.
Learn more on combination here;
https://brainly.com/question/12468032