The formula for percentage error is:
\(\sf{Percentage~ error= \frac{|Approximate ~-~ Actual|}{|Actual|}}\)
Ross got the approximate area as 12, while the actual area was 11.8. So, let's plug it in to the formula.
\(\sf{Percentage~ error= \frac{|Approximate ~-~ Actual|}{|Actual|}= \frac{|12-11.8|}{|11.8|}= \frac{|0.2|}{|11.8|}= \frac{0.2}{11.8} \approx 0.0169 }\)
Multiply 0.0169 by 100 to make it into a percent.
0.0169 * 100 = 1.69%
Ross's percentage error is 1.69%.
