I think perhaps you have not approached this is the right way. But I am making a bit of an assumption about the effect you wanted.
In order to make your footage look fast or slow but still remain in sync you need to adjust both the speed of audio playback and shooting frame rate at the same time by a corresponding amount.
As an example, say you wanted your shots to appear slow motion, lets say half speed, but be in sync and your usual frame rate is 25fps.
You would shoot at 50 fps (double speed) and you would have to speed up the playback track by the same amount.
That way when both were slowed down again, the audio would be at normal speed and the pictures would apparently be at half speed but remain in sync.
What you have done is not adjust the camera shooting speed only the audio playback speed.
So although your artist was singing to playback slower than usual the only way that you can make it fit the track is by speeding it back up by the same amount you slowed it down. This simply cancels out the change in audio speed.
As Andrew says your maths is wrong – you need to speed it up by 11.1111% to return to 100% speed.
However this will just return it to “normal speed” and not really give you the effect I assume you were looking for.
best wishes
Neil
http://www.patience.tv