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The ratio of ages of two persons A and B is 3 ∶ 4 and that of ages of B and C is 4 ∶ 5. If the average of all three is 40 years. What is B's age?
1.  20 years
2. 30 years
3.  40 years
4.  50 years

1 Answer

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Best answer
Correct Answer - Option 3 :  40 years

Given:

Average age = 40 years

Formula used:

Average = Sum of all the terms/Total number of terms

Calculation:

A ∶ B = 3 ∶ 4

And, B ∶ C = 4 ∶ 5 

Then, A ∶ B ∶ C = 3 ∶ 4 ∶ 5

Let the age of A, B and C be 3x, 4x and 5x

Sum of ages of all the persons = 3x + 4x + 5x = 12x

Average = 12x/3 = 4x

⇒ 4x = 40 

⇒ x = 10 

∴ The age of B is 40

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