0
0

Age Difference Remains Constant

Introduction

In aptitude tests, age-related questions are very common. Among them, one of the simplest patterns is the Age Difference Remains Constant rule.

This pattern looks easy - and it really is - but if you understand it well, you can solve questions quickly and with full confidence. Let’s break it down step-by-step, learn the logic, and solve an example together.

Pattern: Age Difference Remains Constant

Pattern

The golden rule in age problems: The difference between two people’s ages never changes.

If A is 6 years older than B today, A was still 6 years older than B ten years ago. Similarly, A will remain 6 years older even twenty years from now.

We can write it simply as:

Younger = Older - gap
Older = Younger + gap

Step-by-Step Example

Question

The difference between the ages of Rahul and Neha is 5 years. Rahul is older. Rahul is 20 years old now. What will be Neha’s age after 7 years?

Options:

  1. 20
  2. 22
  3. 24
  4. 19

Solution

  1. Step 1: Identify who is older and the gap.

    Rahul is older than Neha by 5 years.
    → Age gap = 5.

  2. Step 2: Write Neha’s present age.

    Rahul’s present age = 20.
    Neha’s present age = Rahul’s age - gap.
    → Neha = 20 - 5 = 15.

  3. Step 3: Find Neha’s age after 7 years.

    Neha’s future age = Present age + 7.
    → Neha = 15 + 7 = 22.

  4. Final Answer:

    22 → Option B

  5. Quick Check:

    Rahul’s age after 7 years = 20 + 7 = 27.
    Neha’s age after 7 years = 22.
    Difference = 27 - 22 = 5 ✅ (matches the gap)

Quick Variations

If the question asked “How old was Neha 4 years ago?”, subtract 4 from Neha’s current age: 15 - 4 = 11.

If Rahul’s age was unknown but Neha’s was given, we use: Older = Younger + gap.

Trick to Always Use

  1. Step 1: Find the gap.
  2. Step 2: Write relation.
  3. Step 3: Substitute values.
  4. Step 4: Move forward/backward in time.
  5. Step 5: Verify the gap remains constant.

Summary

Summary

  • Identify who is older and the exact difference (gap) between their ages.
  • Write the relation using the gap (Younger = Older - gap or Older = Younger + gap).
  • Substitute the known values into the relation to find the missing age.
  • Adjust for past or future years by adding/subtracting the required number of years.

Example to remember:
Master this rule, and you’ll handle many age questions with ease!

Practice

(1/5)
1. The difference between the ages of Arun and Bala is 6 years. If Arun is 20 years old, what is Bala’s age?
easy
A. 12
B. 14
C. 26
D. 18

Solution

  1. Step 1: Identify who is older and the gap.

    Arun is older by 6 years.

  2. Step 2: Write the relation.

    Bala = Arun - gap.

  3. Step 3: Substitute values.

    Bala = 20 - 6 = 14.

  4. Final Answer:

    14 → Option B

  5. Quick Check:

    20 - 14 = 6 ✅
Hint: Younger = Older - gap.
Common Mistakes: Some learners mistakenly add the gap instead of subtracting.
2. Rahul is 25 years old. His sister Neha is 5 years younger. What will be Neha’s age after 10 years?
easy
A. 20
B. 25
C. 30
D. 35

Solution

  1. Step 1: Find Neha's present age.

    Neha = 25 - 5 = 20.

  2. Step 2: Move forward 10 years.

    Neha = 20 + 10 = 30.

  3. Final Answer:

    30 → Option C

  4. Quick Check:

    Rahul = 35, Neha = 30 → gap = 5 ✅
Hint: Find present age first, then add/subtract years.
Common Mistakes: Forgetting to compute present age before shifting years.
3. The age difference between a father and son is 30 years. If the father is 40 years old, how old is the son?
easy
A. 10
B. 15
C. 20
D. 25

Solution

  1. Step 1: Identify the gap.

    Father is 30 years older than son.

  2. Step 2: Subtract.

    Son = 40 - 30 = 10.

  3. Final Answer:

    10 → Option A

  4. Quick Check:

    40 - 10 = 30 ✅
Hint: Subtract the gap from the elder's age.
Common Mistakes: Accidentally adding the gap to the younger age.
4. Two friends differ in age by 4 years. If the younger one is 16, what is the age of the older one after 6 years?
medium
A. 20
B. 22
C. 24
D. 26

Solution

  1. Step 1: Find present older age.

    Older = 16 + 4 = 20.

  2. Step 2: Move forward 6 years.

    Older = 20 + 6 = 26.

  3. Final Answer:

    26 → Option D

  4. Quick Check:

    After 6 years: younger = 22, older = 26 → gap = 4 ✅
Hint: Add gap to younger's age to get older's present age, then shift years.
Common Mistakes: Forgetting to add the gap before adding future years.
5. The difference between the ages of Priya and her brother is 8 years. If Priya is 24, how old was her brother 5 years ago?
medium
A. 11
B. 13
C. 16
D. 21

Solution

  1. Step 1: Find brother's current age.

    Brother = 24 - 8 = 16.

  2. Step 2: Move back 5 years.

    Brother 5 years ago = 16 - 5 = 11.

  3. Final Answer:

    11 → Option A

  4. Quick Check:

    Priya then = 19, brother then = 11 → gap = 8 ✅
Hint: Compute current ages first, then shift backward/forward.
Common Mistakes: Subtracting years from the wrong person (e.g., Priya instead of brother).

Mock Test

Ready for a challenge?

Take a 10-minute AI-powered test with 10 questions (Easy-Medium-Hard mix) and get instant SWOT analysis of your performance!

10 Questions
5 Minutes