Question

(5. The average age of 3 sisters is 15. If the ages of 2
sisters are 12 years and 15 years, the age of the third
sister is
(A) 21 years
(B) 17 years
(C) 18 years
(D) 16 years
​

Answer 1

Answer:

18 years

Step-by-step explanation:

(12+15+18)/3=15

Answer 2

$\huge\underbrace\mathfrak\color{lime}{ †\: Question:–}$

The average age of 3 sisters is 15. If the ages of 2 sisters are 12 years and 15 years, the age of the third sister is-

$\huge\underbrace\mathfrak\color{lime}{ †\: Answer:–}$

C) 18 years

Given ;

The average age of 3 sisters is = 15

If the ages of 2 sisters are = 12 years and 15 years

To find ;

The age of the third sister is = ?¿

Now ;

Let fîrst sister age be = x = 12

Let second sister age be = y = 15

Let Third sister age be = z

So let the ages be x , y , z

Here ;

The average age of 3 sisters is 15.

$~~~~~~~~~~~~~~ \frac{x + y + z}{3} = 15$

$~~~~~~~~~~~~~~ \frac{12 + 15 + z}{3} = 15$

$~~~~~~~~~~~~~~ 12 + 15 + z = 15 × 3$

$~~~~~~~~~~~~~~ 27 + z = 45$

$~~~~~~~~~~~~~~ z = 45 - 27$

$~~~~~~~~~~~~~~ z = 18$

So the age of third sister is 18 years