Verified answer

Turning this into an equation is the first problem. The goal here is to find the person's current age, we'll call that Age. We also know something about their age in the past, we'll call that Past.

What do we know so far?

Their age in the past is half their current age: Past = Age / 2.

Their age in the past is ten years ago: Past = Age - 10.

Here we have two equations, and only two unknown variables, Past and Age. Now let's see if we can get rid of one of the variables. Let's look at our first equation:

Past = Age / 2

Do we already know another way to define Past, without adding any more variables? We do, since we know that Past is equal to Age - 10. So let's get rid of Past in this equation by replacing it with this.

Age - 10 = Age / 2

Now we only have one equation and one variable. Time to solve for Age. This means getting Age on one side, and everything else on the other side. Remember that anything you do to one side has to be done to both, or else it's not equal any more.

Age - 10 = Age / 2

Multiplying both sides by 2 gives us:

2 (Age - 10) = 2 (Age / 2)

2Age - 20 = Age

Now we need to get that -20 out of there. Let's add 20 to both sides.

20 + (2Age - 20) = 20 + Age

2Age = 20 + Age

Now let's get all the Ages on one side.

2Age - Age = (20 + Age) - Age

Age = 20

And there's your answer. Remember the steps:

1) Write down an equation for every piece of information you know.

2) Get rid of variables by replacing them with something they're equal to.

3) Once you have only one equation left, get the variable you want alone on one side.