Resto Druid - Rejuvenation - Idol of Awakening and Spark of Hope

Hello Fellow Druids!

I'm having trouble with my 7th grade math and I cannot figure it out.

Rejuvenation specced 13/0/58 Resto Tree Spec costs 446mana
Idol of Awakening reduces mana cost of Rejuvenation by 106mana
Spark of Hope reduces the base mana cost of all spells by 42mana

Rejuvenation costs 446mana - With Idol of Awakening (-106mana..) on, it now costs 371mana.. That's 31mana to much?

Rejuvenation costs 446mana - Spark of Hope (-42mana..) on, it now costs 416mana.. That's 12mana to much?

Rejuvenation costs 446mana - With Idol of Awakening (-106mana) and Spark of Hope (-42mana) on it now costs 341mana.. That's 43mana to much?

Who can explain to me how this shít works? I've tried to google it and i cannot find anything about it.

Thanks in advance!

//Daniel

Because those items reduce the "base cost" of the spell.

Rejuvenation base cost (aka with no talents) = 629 mana

So: 629 - 106 (idol) - 42 (trinket) = 481 mana cost.

Now applies talents (20% from http://wotlk.cavernoftime.com/spell=65139 and 9% from http://wotlk.cavernoftime.com/spell=16847)
481*0,71= 341 mana

Makes sense on the Spark of Hope since it says: Reduces the base mana cost of all spells
Doesnt make sense with the idol as it clearly says it reduces the mana cost by 106.

But thanks for it, now i know why at least! Cheers!