Correct Answer - Option 4 : 68 years

**Given:**

Average age of A, B, and C, 4 years ago = 34 years

Present average age of A and B = 28 years

Average age of C and D after 2 years = 65 years

**Formula used:**

Average = Sum of units/Number of units

**Calculation:**

Sum of age of A, B, and C, 4 years ago = 34 × 3 = 102 years

Present sum of their ages = 102 + (3 × 4) years

⇒ 102 + 12 years

⇒ 114 years

Now, Sum of age of A and B = 28 × 2 years

⇒ 56 years

Age of C = (114 – 56) years

⇒ 58 years

Age of C after 2 years = 60 years

Sum of age of C and D after 2 years = (65 × 2) years

⇒ 130 years

Age of D after 2 years = (130 – 60) years

⇒ 70 years

Present age of D = (70 – 2) years

⇒ 68 years

**∴ The average age of D is 68 years**