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

By mistake = x/10 

Actual value = x * 10 

% Change =  $\frac{10x-\frac{x}{10}}{10x}\times 100 = \frac{99}{100}\times 100$  = 99% (negative)

Since actual value is greater than the wrong value.