The average age of Raj and his father is 45 years. If the ages of the father and the grandfather of Raj are respectively two and three times that of Raj, then the age of Raj's grandfather is

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  1. 75 years
  2. 90 years
  3. 81 years
  4. 84 years

Answer (Detailed Solution Below)

Option 2 : 90 years
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Given:

The average age of Raj and his father is 45 years.

The age of Raj's father is 2 times Raj's age.

The age of Raj's grandfather is 3 times Raj's age.

Formula used:

Let Raj's age be R.

Father's age = 2R

Grandfather's age = 3R

Average age = (Raj's age + Father's age) / 2

Calculation:

Average age of Raj and his father = 45

⇒ (R + 2R) / 2 = 45

⇒ 3R / 2 = 45

⇒ 3R = 45 × 2

⇒ 3R = 90

⇒ R = 90 / 3

⇒ R = 30

Grandfather's age = 3R

⇒ Grandfather's age = 3 × 30

⇒ Grandfather's age = 90

∴ The correct answer is option (2).

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