Mean or average value
The mean value of a number of data x={x1,x2,x3,...,xn} is calculated with the formula:
[tex]x_m=\frac{\sum^n_1x_i}{n}=\frac{x1+x2+x3+\cdots+xn}{n}[/tex]
We are given four values in the table (x1, x2, x3, and x4), we need to find the value of x5 so the mean is 90. Let's use the formula and the data
[tex]\frac{87+94+91+84+x5}{5}=90[/tex]
Multiplying by 5:
[tex]87+94+91+84+x5=90\cdot5=450[/tex]
Solving for x5:
[tex]x5=450-87-94-91-84[/tex]
Operating:
x5 = 94
Regina should sell 94 books on day 5
