Question

Explain how you solve each problem. Show all your work. Marissa is 3 years older than her younger brother. Her older brother is twice as old as her younger brother. Her older brother is 18. How old are Marissa and her younger brother?

Answer 1

Marissa's age = 12

Younger brother's age = 9

Explanation:

Let age of Marissa be x, and her younger brother's y.

Equations formed :

1. x = y + 3
2. 2y = 18

Finding age of younger brother using Equation 2 :

⇒ 2y = 18

⇒ 2y/2 = 18/2

⇒ y = 9 years old

Substituting y in Equation 1 :

⇒ x = y + 3

⇒ x = 9 + 3

⇒ x = 12 years old

Marissa's age = 12

Younger brother's age = 9

Answer 2

Note that:

• Marissa=
  `x + 3`
• Older brother= 18
• Younger brother=
  `\frac {18}{2}`

To find:

The age of Marissa and her younger brother.

Solution:

Younger brother:

We know that the older brother's age is 18 and he is twice older than the younger brother.

Let the unknown be "x"

`x=(18)/(2)`

`\large\boxed{\sf{x=9 \: years}}`

Marissa:

Now, we know that the younger brother's age is 9 and Marissa is 3 years older than him.

Let the unknown be "x"

`x=9 + 3`

`\large\boxed{\sf{x=12 \: years}}`

Therefore, Marissa is 12 and her younger brother is 9