Answer
He must shoot less than or equal to 77.
The solution set is {x|x $\leq$ 77}.
Work Step by Step
Let x represent the score on the last day.
The average for the five days is $\frac{82+84+78+79+x}{5}$.
Because the average for the five days needs to be 80 or less, we solve the following inequality.
$\frac{82+84+78+79+x}{5}$ $\leq$ 80
Multiply both sides by 5.
82+84+78+79+x $\leq$ 400
323 + x $\leq$ 400
x $\leq$ 77
He must shoot less than or equal to 77.
The solution set is {x|x $\leq$ 77}.
