Question

The average age of our family of 4 is 35. Excluding me,the average age is 40. Find my age

Answer 1

Hi there!
Here's the answer:

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¶ $Average A= \frac{Sum\: of\: Observations\: S}{No.\: of\: Observations\: n}$


Given,
No. of observations(persons in family) n1 = 4
Average A1 = 35
=> Sum = Average × No.
=> S1 = A1 × n1
=> S1 = 35 × 4
=> S1 = 140

When one observation(person's age) is excluded n2= 3
Average A2 = 40
=> Sum = Average × No.
=> S2 = A2 × n2
=> S2 = 40 × 3
=> S2 = 120

Age of excluded observation (person) = S2 - S1 = 140 - 120 = 20

•°• Required Age = 20 years


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Hope it helps