Question

The average age of a and b 10 years ago was 20 . The average age of a b and c today is 30 so what will be the age of c

Answer 1

Hi there!
Here's the answer:

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¶ Average = $\frac{Sum\: of\: observations}{No.\: of\: Observations}$


Let present age of A, B & C be x, y, z respectively

10 years ago,
Age of A = x-10
Age of B = y-10



Given,
Average of Ages of A and B = 20

=> $\frac{x-10+y-10}{2} = 20$

=> x+y-20 = 40

=> x+y = 60 ---------------- (1)


Also Given,
Average of present ages of A,B and C = 30

=> $\frac{x+y+z}{3} = 30$

=> x+y+z = 90 --------------(2)

Substitute (1) in (2)

=> 60 + z = 90
=> z = 30


•°• Present Age of C = z = 30 years.


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