Answer:
Step-by-step explanation:

What you can do is multiply 400*20= 8,000. From here, we know that 399*20 is just one less group of 20 than 400. Therefore, we can subtract (1*20) from 8,000 to get the final answer.
8000-20=7980
Hope this helps!
Answer: 24 & 72
Step-by-step explanation: 24 + 72 = 96
24 x 72 = 1728
Solution: We are given the population mean 
Now, in order to find which shift's mean is closest to population mean, we will find the mean of each shift.
The mean of shift 1 is:

The mean of shift 2 is:

The mean of shift 3 is:

The mean of shift 4 is:

We clearly see the mean of shift 2 is close to the population mean. Hence the option B) Shift 2 is correct.