Although I grudgingly excuse JM's incorrect use of %, I cannot excuse its use in a mathematical formula.
% means that whatever number preceeds it, move the decimal two places to the right. i.e. 100% = 1, 57%=0.57
The formula you posted is actually just:
mag. bal. + (mag. skill% * mag. bal.)
If you follow JM's example, then 100% = 200 or 2
(i.e. Moving March 1 gives 20% run speed, but it should say 120%, since 20% would be an 80% reduction in run speed)