A number 42 was misread as 24. find the reading error in percent.
${\text{A}}{\text{. }}$45%
${\text{B}}{\text{. }}$25%
${\text{C}}{\text{. }}$42.8%
${\text{D}}{\text{. }}$36.8%

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Hint: We have to find a reading error in percent. For which first we have to find error in reading then we will find the percentage of it by formula. Percentage error = $\dfrac{{{\text{error}}}}{{{\text{correct number}}}} \times 100$

Complete step-by-step answer:
We have given
Correct number = 42
Misread as = 24
Error = ( correct number – misread )
Error = 42 – 24 = 18
Now we have to find error percentage using formula
Percentage error = $\dfrac{{{\text{error}}}}{{{\text{correct number}}}} \times 100$
Percentage error = $\dfrac{{18}}{{42}} \times 100 = 42.8\% $
Hence option C is the correct option.

Note: Whenever we get this type of question the key concept of solving is we should just have knowledge of percentage and basic knowledge of what is error. An error is something you have done which is considered to be incorrect or wrong, or which should not have been done.