In engineering economics, which statements correctly describe an annuity (uniform payment series) used in present worth and capital recovery calculations?

Introduction / Context:
Annuities are foundational to time-value-of-money analysis. They represent uniform payments (or receipts) made at regular intervals—monthly, quarterly, yearly, etc.—and underpin formulas for present worth, future worth, and capital recovery, which are vital in project evaluation and life-cycle costing.

Given Data / Assumptions:

• Annuity refers to equal payments A at equal intervals.
• Intervals can be any length but must be consistent across the series.
• Used in standard engineering-economy factors such as P/A and A/P.

Concept / Approach:

An annuity is termed a uniform or equal-payment series. The timing must be consistent (e.g., every year). Whether payments occur at period end (ordinary annuity) or period beginning (annuity due), uniformity of amount and spacing defines the series and allows closed-form factors to be applied.

Step-by-Step Solution:

Verification / Alternative check:

Textbook factor tables (P/A, F/A, A/P, A/F) and spreadsheet functions (PMT, PV, FV) all assume a uniform series with constant period length and equal amounts.

Why Other Options Are Wrong:

• Any single statement alone omits other essential attributes.
• 'None of these' is incorrect since all definitions align with standard usage.

Common Pitfalls:

• Confusing gradient series (which change by a fixed amount each period) with annuities.
• Mixing period length midstream, which invalidates standard factors.

Final Answer:

All the above.