Calculating variance for central limit theory question

Question

I was struggling with the following question

question

So the mean I can take as 120 * 0.20 = 24 I'm assuming The variance I thought I could take similarly using Var(X) = np(1-p) which gives me a value of 4.8

However, this doesn't lead me to the answer given in the image above (in red)

Am I calculating one of these wrong?

Many thanks in advance

Answer 1

Guide:

If $X$ denotes the number of petunias then $X$ has binomial distribution with parameters $n=120$ and $p=0.2$.

To be found is $P(X\leq 30)$ and you can estimate this by calculation of $P(Y\leq 30)$ where $Y$ has normal distribution with parameters $\mu=np$ and $\sigma^2=np(1-p)$.