I think asking politicians trivial maths questions achieves nothing, really, anyway, so I can't say I begrudge Osborne, Balls, Nociky Morgan etc their choice to dodge it. I would probably rather do the same myself in most cases, at least in the typical
"What do you do?"
"I'm a mathematician/ physicist."
"Oh so what's 11*13 then?"
You either know the answer straightaway or you just seem to end up being assumed to be incompetent. Rather unfair because it has barely anything to do with what most mathematicians do. Ditto Chancellors, whose job isn't to know 8*7 but to understand economic policy.
Mind, most of them fail at the latter, as well, but at least that's a relevant failing.