Last month John had $240 in his savings account. He got money for his birthday and now he has $320. What is the percent of change for his account?

Margie is practicing for an upcoming tennis tournament. her first serve is good 20 out of 30 times on average. margie wants to know the estimated probability that her first serve will be good at least four of the next six times she serves. how could she design a simulation for this scenario?