"Tools are a sound investment that result in..." or "...that results in..."?

If I am using the sentence, "Tools are a sound investment that result(s) in significant gains in productivity.", do I use result or results? I'm unsure if the verb "result(s)" is acting on the noun "investment" or the noun "tools".

Solution 1:

I would use "result", because in my opinion it refers to the noun "tools".

But another suggestion I would like very much: "Tools are a sound investment resulting in significant gains in productivity"

Solution 2:

The correct answer is "results", because its subject is "investment".

But if you want to say that tools result in gains (rather than speaking of an investment that results in gains), there are:

• Drew's paraphrase "Tools are a sound investment. They result in..."
• Tools are a sound investment, and result in...

Solution 3:

Reduce the sentence to its essentials:

Tools [result/results] in gains.

The choice is plainly result:

Tools are a sound investment that result in significant gains in productivity.