23. Exemplar exercise problems III

1. In a school only, $3$ out of $5$ students can participate in a competition. What is the probability of the students who do not make it to the competition?

 

2. Ram put some buttons on the table. There were $4$ blue, $7$ red, $3$ black and $6$ white buttons in all. All of a sudden, a cat jumped on the table and knocked out one button on the floor. What is the probability that the button on the floor is blue?