Not receiving total 40% edu decrease

Recently i started a course where for the first time I had the principal 10% edu decrease perk, full edu decrease merits and the WSSB BB. The course i chose to start was a 2 week one and it took it down to 9 days and 1 hour which is not 40% which is weird. Idk if this is a bug or just me but would like some closure on this,
Cheers SpAdes123

it isnt a total 40% reduction (don't stack) if you calculate them all separately and it will be correct.

Change your reduction times to percent of total, so -10% = 0.9

Then multiply them all out

Reduced timed = total time * (reduc1) * (reduc2)...