'Getting probabilities from a bimodal distribution in R

I'm trying to solve the following task: Exam scores of students have a bimodal distribution, where

mode = 30 and 60
mean = 45
standard deviation = 25

What is the probability that the average score of 5 randomly selected students is greater than 45?

In a normal distribution and for one student, the code would be

pnorm(45, mean=45, sd=25, lower.tail = FALSE)

Any suggestions to solve the task?

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