Question

Four years ago the average age of A,B and C was 25 years. Five years ago the average age of B and C was 20 years. A's present age is ​

Answer 1

Answer:-

Given:

Four years ago average age of A , B & C was 25 years.

Let the ages of A , B , C be A , B , C years.

• Age of A before 4 years = (A - 4) years.

• Age of B before 4 years = (B - 4) years.

• Age of C before 4 years = (C - 4) years.

We know that,

Average = Sum of observations/Number of observations.

Here,

• Sum of observations = A - 4 + B - 4 + C - 4 = (A + B + C - 12) years.

• Number of observations = 3.

So, (A + B + C - 12)/3 = 25

⟹ A + B + C - 12 = 3 * 25

⟹ A + B + C = 75 + 12

⟹ A + B + C = 87 -- equation (1)

Also given that,

Average age of B & C before 5 years was 20 years.

⟹ (B - 5 + C - 5)/2 = 20

⟹ B + C - 10 = 2 * 20

⟹ B + C = 40 + 10

⟹ B + C = 50 -- equation (2)

Subtract equation (2) from equation (1).

⟹ A + B + C - (B + C) = 87 - 50

⟹ A + B + C - B - C = 37

⟹ A = 37 years

∴ A's present age is 37 years.

Answer 2

Answer:

$\green\bigstar$ Given $\green\bigstar$

$\mapsto$ Four years ago the average age of A, B and C was 25 years . Five years ago the average age of B and C was 20 years .

$\green\bigstar$ To Find $\green\bigstar$

$\mapsto$ What is the present age of A's.

$\green\bigstar$ Solution $\green\bigstar$

➕ Let the present age of A,B,C be x, y, z years respectively.

✴️ According to the question,

$\implies$ $\dfrac{(x - 4) + (y - 4) + (z - 4)}{3}$ = 25

$\implies$ x + y + z - 12 = 75

$\implies$ x + y + z = 75 + 12

$\implies$ x + y + z = 87 ....... Equation no 1

Again,

$\implies$ $\dfrac{(y - 5) + (z - 5)}{2}$ = 20

$\implies$ y + z - 10 = 40

$\implies$ y + z = 40 + 10

$\implies$ y + z = 50 ..... Equation no 2

➡️ From the equation no (1) and (2) we get,

$\implies$ x = (x + y + z) - (y + z)

$\implies$ x = 87 - 50

$\dashrightarrow$ x = 37 years.

$\therefore$ The present age of A's is 37 years.

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Step-by-step explanation:

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