Answer:
The sale this month = 79
Step-by-step explanation:
Let the amount he needs to sell this month = x
[tex]Average = \frac{sum\ of\ individual\ data\ }{number\ of\ entries}[/tex]
[tex]Average= \frac{90\ +\ 45\ +\ 103\ +\ 68\ +\ x}{5}[/tex]
Note that number of entries = number of months = 5
To maintain an average sales of 77, the amount of sale in month 5 is determined as follows:
[tex]77 = \frac{306\ +\ x}{5} \\cross-multiplying\\77\ \times\ 5\ = 306\ +\ x\\385 = 306\ +\ x\\x =385\ -\ 306\\x = 79[/tex]