Alebraic concepts Who is older?

Question

A child is 1/3 the age of an older sister. The sum of both childern is 16.

How old is the younger child?

10

4

2

8

6

I was thinking 8, ethier way what kind of formla would I use to solve this, Was I right?

Answer 1

Let the older sister be (x)

The younger child is 1/3x

The sum of their ages is 16

So you have

x + 1/3x = 16

        4/3x=16    (3/3x + 1/3x) = 4/3x combine the x terms

            x=12    (3/4 x 16)  times each side by 3/4

The older sister is 12 and the younger sister is 4

Answer 2

The equation below is formed from the problem statement:

1/3*S + S = 16

1/3*S is the age of the child; which is one third the age of the sister. Because the sum of their ages is 16, adding S to 1/3*S will equal 16.

This equation can be re-written as:

4/3*S = 16

Solving for S gives 12.

1/3 of 12 is 4.

12 + 4 = 16

The younger child is 4.