Let's see,
If Shade is correct about barbarian speed being 1.1 base speed then we can set a barb's normal speed as 110.
A 40% increase due to haste would be 110 * .4 = 44%.
A 50% increase due to speed boost would be 110 * .5 = 55%.
All this added together gives 110 + 44 + 55 = 209
Take out the original base run speed and the net increase is 109%.
In the second case the base speed is normal so 100.
Each percentage increase is simply its own self.
Add this all together gives 100 + 40 + 50 + 15 = 205%.
Take out the original base run speed and the net increase is 105%.
It is essentially a multiplication problem when calculating the individual increases and an addition problem when determining the total stacked values.