Twenty years ago, my age was one-third of my present age. What is my present age (in years)?

Introduction / Context:
Translate a past fraction-of-present statement into an equation linking present age x and x − 20, then solve for x straightforwardly.

Given Data / Assumptions:

• Let present age = x years
• x − 20 = x / 3

Concept / Approach:
Rearrange the linear equation to isolate x.

Step-by-Step Solution:

Verification / Alternative check:
Twenty years ago age = 10; 10 is one-third of 30, correct.

Why Other Options Are Wrong:
25, 35, 40 fail the one-third condition when tested.

Common Pitfalls:
Setting x − 20 = (1/3)(x − 20) instead of x/3; the comparison is with the present age, not past age.

Final Answer:
30 years.