The net present value (NPV) rule can be best stated as:

An investment should be accepted if, and only if, the NPV is exactly equal to zero.

An investment should be rejected if the NPV is positive and accepted if it is negative.

An investment should be accepted if the NPV is positive and rejected if its is negative.

An investment with greater cash inflows than cash outflows, regardless of when the cash flows occur, will always have a positive NPV and therefore should always be accepted.