Item Modifiers seems like not accurate, not sure whether is configuration issues?

[shoku2003]

Hi i would like to as on item modifiers,

i got created an product A which is selling at price eg: $15
i did a modifier and which will give some price reduction if customer purchase in bundle of 5 which is at price of $55

but instead if showing $55 it showing me $70 which made me in confused. can any pro's guide me on how to configure the back end for the item modifier?