Which Probabilty Formula?

#1
More than 200 billion grocery coupons are distributed each year for discounts exceeding $84 billion. However, according to a report in USA Today, only 3.2% of the coupons are redeemed. If a company distributes 5000 coupons, what is the probability that:


(a) at least 100 coupons are redeemed?

Just need to know which formula I should use to solve this problem?
 
#2
approximate using the normal distribution

Here,
n=5000
p=0.032
You are looking for the probability that more than 100 coupons are redeemed. The appropriate way to solve this problem is using the binomial distribution.
However, because n is large we can approximate the binomial distribution with a normal distribution with mean=np and variance=np(1-p). From there you are looking to solve for P(X>100).
Hope this helps!!
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More than 200 billion grocery coupons are distributed each year for discounts exceeding $84 billion. However, according to a report in USA Today, only 3.2% of the coupons are redeemed. If a company distributes 5000 coupons, what is the probability that:


(a) at least 100 coupons are redeemed?

Just need to know which formula I should use to solve this problem?