# I am 4 times as old a her. She was born when I was 39.

#### suzibel

##### New member
I am trying to help my daughter with her algebra homework. Ive come to a question where i cannot help her and would appreciate any help.

the question:-

I am four times as old as my daughter. She was born when I was 39, how old am I now?

I have worked out the answer is 52, just by using multiples of 4 etc.

My problem is she has to work it out using algebra and show her workings out. Ive tried but come to a dead end.

I would like help asap as homework has to be in tomorrow.

thanks

Suzibel

#### soroban

##### Elite Member

Hello, Suzibel!

There are a number of approaches to this problem.
. . Here's one of them . . .

I am four times as old as my daughter.
She was born when I was 39.
How old am I now?

$$\displaystyle \text{Let }x = \text{number of years since you were 39 years old.}$$

$$\displaystyle \text{Back then, you were 39 and your daughter was 0.}$$

$$\displaystyle \text{Now (}x\text{ years later), you are } 39 + x \text{ and your daughter is }x\text{ years old.}$$

$$\displaystyle \text{And you are 4 times as old as your daughter: }\;39 + x \;=\;4x$$

. . $$\displaystyle \text{Solve for }x:\;\;x \:=\:13$$

$$\displaystyle \text{So, 13 years ago, you were 39.}$$

$$\displaystyle \text{ Therefore, you are: }\:39 + 13\:=\:{\bf52}\text{ years old now.}$$