Cant multiply by a decimal when upgrading the cost of an upgrade?

[X-maul]

I am trying to make the cost of my upgrade increase by 175% each upgrade, I'm trying to do this by making the upgrade affect the ability that upgrades it, and multiplying the cost by 1.75.

But the thing is that I cant multiply by anything between 1 and 2? no punctation allowed?
Is this a bug, or is there a way to solve this?

EDIT: Btw, I fixed this by changing to XML view and changed it from there, but I just wonder why this happens.
EDIT2: It did not solve the problem to edit it in XML View, it simply cant be a decimal