The probability of a certain event happening is given by the ratio between the amount of possibilities with this event as the outcome and all possible events. For example, on our first situation, we want to know the probability of rolling a number less than or equal to 6 on a standard six-sided dice, numbered from 1 to 6.
We have 6 numbers on a six-sided dice, and all of them are less than or equal to 6, therefore, the probability of this event is 100%.
For the second situation, we want to know the probability of spinning a spinner divided into four equal-sized sections colored red/green/yellow/blue and landing on blue or yellow. We have a total of 4 possibilities(red/green/yellow/blue), and the desired outcome represents 2 possibilities(blue or yellow), therefore, the probability is given by the ratio of those two quantities.
The probability of this event is 50%.
For the third situation, we have 5 tickets from a total of 100 tickets, therefore, the probability is 5%.
For the last situation we have a bag with 19 strawberry chews and 1 cherry chew. This means we have a total of 20 possibilities, however, we want to pull a pineapple chew from the bag, and since there are no pineapple chews inside the bag we have 0 of this outcome. The ratio between 0 and 20 is 0, thus, the probability of reaching into a bag full of 19 strawberry chews and 1 cherry chew without looking and pulling out a pineapple chew is 0%, and this is the less likely(impossible, actually) situation to happen.