A boy found the answer for the question "subtract the sum of \(\frac{1}{4}\) and \(\frac{1}{5}\) from unity and express the answer in decimals" as 0.45, the percentage of error in his answer was:

18.18%

ATQ,

1 - (\(\frac{1}{4}\) + \(\frac{1}{5}\)) = \(\frac{11}{20}\) = 0.55

Now,

        Actual          :         Wrong

          0.55          :          0.45

             11          :          9

Percentage of Error = \(\frac{11 - 9}{11}\) × 100% = \(\frac{200}{11}\)% = 18 \(\frac{2}{11}\) % = 18.18 %