Speed Limits....

....naughty me, had to sit a speed awareness course recently - got me wondering if, with today's modern cars speed limits are scentifically speaking, worthwhile?

ALSO

During that time the instructor says, if you hit a child a 30mph, 80% of living....but, at 40mph 80% chance of dying, and i'm sure a similar statistic used to be included in road safety adverts.

Fair enough - BUT

You can't hit the same child at 40mph, that you would have hit at 30mph....you'd be further down the road, and the child would walk out safely behind you....

Am I wrong? I wonder what the math would show....