Today is Varun's birthday. One year from today, he will be twice as old as he was 12 years ago. How old is Varun today?

Introduction / Context:
This is a standard algebraic age problem often seen in quantitative aptitude exams. You are given information about Varun's age at different times relative to today: one year in the future and twelve years in the past. The relationship between these ages allows you to set up an equation and solve for Varun's present age. Such problems train you to translate verbal conditions into algebraic expressions.

Given Data / Assumptions:

• Let Varun's present age be x years.
• One year from today, his age will be x + 1 years.
• Twelve years ago, his age was x - 12 years.
• We are told that one year from now, his age will be twice his age twelve years ago.

Concept / Approach:
The main idea is to convert the statement “one year from today he will be twice as old as he was 12 years ago” into an equation. This gives a linear relationship between x + 1 and x - 12. Solving this linear equation will directly yield the value of x, which is Varun's present age. Once we obtain a candidate value, we also verify it back in the verbal condition.

Step-by-Step Solution:
Step 1: Assume Varun's present age is x years.Step 2: According to the problem, one year from today his age will be x + 1.Step 3: Twelve years ago his age was x - 12.Step 4: The condition is x + 1 = 2 * (x - 12).Step 5: Expand the right-hand side: x + 1 = 2x - 24.Step 6: Rearrange the equation: bring x to one side, 1 + 24 = 2x - x, so 25 = x.Step 7: Therefore, Varun's present age is 25 years.

Verification / Alternative check:
We verify by substituting x = 25 into the original words. One year from today, Varun will be 26 years old. Twelve years ago, he was 25 - 12 = 13 years old. Twice 13 is 26, which matches his age one year from now. Thus, the condition is fully satisfied. None of the other options gives a present age that satisfies this relationship when substituted in the same way.

Why Other Options Are Wrong:
Option A (20 years): One year from now he would be 21, while 12 years ago he would have been 8. Twice 8 is 16, which does not equal 21.
Option B (22 years): One year from now he would be 23, and 12 years ago he would have been 10. Twice 10 is 20, not 23.
Option D (27 years): One year from now he would be 28, and 12 years ago he would have been 15. Twice 15 is 30, not 28.

Common Pitfalls:
A common mistake is to misread the phrase “one year from today” and to set x instead of x + 1 on the left-hand side of the equation. Another mistake is confusing “12 years ago” with “in 12 years”. Always carefully identify which time is in the past and which is in the future before forming the equation. Writing out each step clearly helps avoid sign and time-direction errors.

Final Answer:
Varun is currently 25 years old.