That's not how it works. You get +100% production for the resource, +50% for the Industrious trait, +25% for the Forge, for a total of +175%. So you build 2.75 times faster than without any of those, or 36% of the what the build time would be if you had none (I hesitate to call that "normal", becuase usually you don't try to build most wonders unless you have the matching resource).