The relationship between the number of 12$ dvds you by and the total cost

You are at a restaurant and owe $38 for your meal. you want to leave a 20% tip. how much will your tip be?

Aparticular telephone number is used to receive both voice calls and fax messages. suppose that 25% of the incoming calls involve fax messages, and consider a sample of 25 incoming calls. (a) what is the expected number of calls among the 25 that involve a fax message?

Could someone me with this question i’ve been stuck on it for 20 minutes