We need to work out the z-value of each question to work out the probability
Question a)
We have
X = 5 minutes
The mean, μ = 6.7 minutes
Standard deviation, σ = 2.2 minutes
z-score = (X - μ) / σ = (5 - 6.7) / 2.2 = -0.77
We want to find the probability of z < -0.77 so we read the z-table for the value of z on the left of -0.77 we have the probability P(z< -0.77) = 0.2206
The table is attached in picture 1 below
The probability of assembly time less than 5 minutes is 0.2206 = 22.06%
Question b)
z-score = (10-5) / 2.2 = 2.27
Reading the z-table for P(z<2.27) = 0.9884
The table reading is shown in the second picture below
The probability the assembly time will be less than 10 minutes is 0.9884
We can use this information to find the probability of the assembly time will be more than 10 minutes = 1 - 0.9884 = 0.0116 = 1.16%
Question c)
The value of z between 5 minutes and 10 minutes is
P(-0.77<z<2.27) = P(z<2.27) - P(z< -0.77)
P(-0.77<z<2.27) = 0.9884 - 0.2206 = 0.7678 = 76.78%
