Answer
According to the formula, 49% had an average grade of A in 2010.
The formula overestimates the percent displayed on the graph by 1%.
Work Step by Step
To find x, the number of years after 1980, subtract 1980 from the given year. Substitute for x and use the addition property of equality to solve the equation for p.
$p-0.8x=25$
$p-0.8(2010-1980)=25$
$p-0.8(30)=25$
$p-24=25$
$p-24+24=25+24$
$p=49$
The graph shows the actual percentage was 48%, a difference of 1%. Since the actual number is smaller, the formula overestimates the percentage.
