Complaints about an Internet brokerage firm occur at a rate of 5 per day. The number of complaints appears to be Poisson distributed.

A. Find the probability that the firm receives 3 or more complaints in a day.
B Find the probability that the firm receives 21 or more complaints in a 5-day period.

I got part A, using the Poison distribution, and doing 1-P(0,1 or 2) complaints. For part B, do I have to do 1-P(0 through 20) with the rate being 20 in a 5 day period. Seems pretty tedious. Should I use normal approximation instead?