Andy “Seven Eights” Burnham per Guido Fawkes

Guido Fawkes reports http://order-order.com/2015/08/03/andy-seven-eights-burnham about the intellectual colossus that is Andy Burnham, including that his nickname at school was "seven eights" because according to his mother 'He couldn't remember that seven eights are 56.'  

The report sourced from the Labour supporting Mirror also reports that:

'Before Ed Miliband chose Ed Balls as his Shadow Chancellor, he searched his Shadow Cabinet for an alternative. The FT famously revealed that Burnham was suggested for the job:"But Andy can't do maths," was Mr Miliband's lament.'

If that's the case then why was Andy  Burnham Chief Secretary to the Treasury ahead of the 2008 crash? Possibly he should have been in a less mathematically demanding role, maybe tea maker.