IMO the majority of people saying "I gave it 150%" know perfectly well that this is literally impossible
Sadly, you are incorrect, Dilys. When I was appointing staff 15 years ago, I whittled the applicants down by rejecting all those without degrees (I know - horrid, but pragmatic) and without decent GSEs in Maths & English. Then I threw out all the ones with elementary spellos and bad grammar. It was a negotiating job - it was essential to be able to work out roughly accurate figures on the go - so I asked them to do some simple arithmetic. Out of ten interviewees, there would only be two who showed a basic grasp of percentages: every ... single ... time. I mean basic! One girl got the job because she was the only one out of the ten who could tell me 45% of 200!
I've got to say all my trainees were fantastic. I was proud of them :) What a pity, though, that they required arithmetic training before fulfilling their potential.
I try to talk clients out of using percentages in their promotions, on the obvious grounds that most people don't understand them. Most of them insist ... despite the fact that at least two of them can't do percentages themselves. I'm waiting for someone to instruct me on a 110% discount 
Still, you gotta go with figures of speech. I say "110%" when I know it's impossible. I try to keep my pedantry quiet, in general 