We are told that there is one male snake, and the rest are female.
She needs one vitamin pill for every female snake.
1. If there are 10 snakes, this means that if one is male, the number of female snakes are:
Sine one vitamin pill is needed for each female snake, she would need 9 vitamin pills.
2. If there are 6 snakes, this means that if one is male, the number of female snakes are:
Sine one vitamin pill is needed for each female snake, she would need 5 vitamin pills.
3. If there are X snakes, this means that if one is male, the number of female snakes are:
Sine one vitamin pill is needed for each female snake, she would need (X-1) vitamin pills.