Back to even calculation

Example: If you own $1,000 in stock and that stock loses 15%, now that stock is worth $850. What percentage is needed to get back to even?
 
% of lost / 1-(% of lost)
 
.15/1-.15= 17.76% to get back to even.
 
Another example
If you own $1,000 in stock and that particular stock loses 25%, now that stock is worth $750. What percentage is needed to get back to even?
 
% of lost / 1-(% of lost)
.25/1-.25=33.3% to get back to even.