This is utterly ridiculous. Not ALL kids are fukken stupid, not all kids can't do mental arithmetic. **** it, you don't need to be good at mental arithmetic to be a good mathematician. It's not as though the 'kids of today' can sit the SAME exams that you and others did, no, we must do what we are able to. And as such, devaluing others scores under the notion that 'they are getting easier' is rather ridiculous. saintandy for example, has done very very well in his GCSEs, he'd probably have done fairly well in 'old-style exams', as I also would perhaps, yet we don't have the opportunity to take such things and try to 'own' that which is available to us.
Also, if you were to ask me to do mental arithmetic, I'd fukken do it, and get it right.