I think it still wrong, although one may understand what the other person means.
When we say "faster" or "slower" what we usually mean is that we add/remove the percentage to the original amount, which is often cause of misunderstanding.
"Y is 10% faster than X" means that Y goes at 110% the speed of X
"Y is 10% slower than X" means that Y goes at 90% the speed of X
In particular, "Y is N% slower than X" doesn't mean that "X is %N faster than Y" ! (110% of 90% is not 100%)
For example "Y is 100% slower than X" doesn't mean that "X is double as fast as Y", but that Y is not moving at all.
and "Y is 200% slower than X" means... that Y goes in the other direction ? (Maybe back in time, in this case ?)
When we say "faster" or "slower" what we usually mean is that we add/remove the percentage to the original amount, which is often cause of misunderstanding.
"Y is 10% faster than X" means that Y goes at 110% the speed of X
"Y is 10% slower than X" means that Y goes at 90% the speed of X
In particular, "Y is N% slower than X" doesn't mean that "X is %N faster than Y" ! (110% of 90% is not 100%)
For example "Y is 100% slower than X" doesn't mean that "X is double as fast as Y", but that Y is not moving at all.
and "Y is 200% slower than X" means... that Y goes in the other direction ? (Maybe back in time, in this case ?)