# Math Help - How Many Years Ago?

1. ## How Many Years Ago?

Sean is 20 and his brother is 12. How many years ago was Sean three times as old as his brother?

MY WORK:

20 - x = 3(x)
20 - x = 3x
20 = x + 3x
20 = 4x
20/4 = x
5 = x

Sean's current age is 20.
Sean's age some years ago is 20 - x.

I just found x to be 5.
So, 20 - 5 = 15.
15 is three times more than 5.
So, when Sean was 15 years old, his brother was 5.

Is this correct?

2. Look at your answer. If Sean's brother is 12 now, how could he have been 5 years old five years ago?

Sean's age $x$ years ago: ${\color{red}20 - x}$
Sean's brother's age $x$ years ago: $\color{blue} 12 - x$

Sean's age $x$ years ago was 3 times as old as Sean's brother's age $x$ years ago.

In equations: ${\color{red}20 - x} = 3 \cdot \left({\color{blue}12 - x} \right)$

3. ## 8............

Originally Posted by o_O
Look at your answer. If Sean's brother is 12 now, how could he have been 5 years old five years ago?

Sean's age $x$ years ago: ${\color{red}20 - x}$
Sean's brother's age $x$ years ago: $\color{blue} 12 - x$

Sean's age $x$ years ago was 3 times as old as Sean's brother's age $x$ years ago.

In equations: ${\color{red}20 - x} = 3 \cdot \left({\color{blue}12 - x} \right)$
Is the answer 8 years ago?

4. Well plug it in.

8 years ago, Sean was 12 and his brother was 4. Does that fit your question?

5. ## I guess....

Originally Posted by o_O
Well plug it in.

8 years ago, Sean was 12 and his brother was 4. Does that fit your question?
I guess it does.