Hey all you binomial distribution fanatics out there!

My question is:

The following is my attempt:Let x be a binomial random variable and suppose n= 20, p=0.2. Then P(μ-σ ≤ x ≤ μ+σ) is:

However the correct answer is 0.844I know that:

μ = n*p = 20*0.2 = 4

σ = sqrt(npq) = 1.788

So Im looking for the the range of x being between 2.21 and 5.788

But the binomial distribution chart for n = 20 only shows k values for whole numbers, so what I would be looking for is: (k=5)-(k=3), which is 0.804-0.411=0.393

can someone help me solve this?