A number x is mistakenly divided by 10 instead of being multiplied by 10. what is the percentage error in the result?

Answer: Option A

Actual result = 10x
By mistake it has been divided by 10 = $$\frac{x}{10}$$
%Change = $$\frac{10x-\left(\frac{10}{x}\right)}{10x}$$   × 100 = 99 = -99%
Since, actual value is greater than the wrong value.

Alternatively,
Let, x = 10
Actual result = 10 × 10 = 100
Wrong result = $$\frac{10}{10}$$ = 1
Change = (1 - 100) = -99
% Change = - 99%