If in $$k+1$$ years from now, John will be $$m$$ years old, then how old was John $$t-1$$ years ago?

Now go to the answer choices to eliminate any that do not match your goal value. **Plug In** all variables and eliminate any that do not equal 2.
>A) $$m-k-t = 10-3-5 = \color{blue}{2}$$.
This doesn't automatically mean that A is the answer, since we need to check all five choices. But it does mean we cannot eliminate A yet.
>B) $$m+k-t+2 = 10+3-5+2 = \color{red}{10}$$.
This is not equal to 2. __POE__ this answer choice and move on.
>C) $$m+k-t+1 = 10+3-5+1 = \color{red}{9}$$ .
This is not equal to 2. __POE__ this answer choice and move on.
>D) $$k-m-t+2 = 3-10-5+2$$.
That's going to be negative, and not equal to 2. __POE__ this answer choice and move on.
>E) $$k+t-m = 3+5-10 = 8-10= \color{red}{-2}$$.
This is not equal to 2. __POE__ this answer choice.
Answer choice A is the only answer choice that is equal to 2 for $$k=3$$, $$m=10$$, and $$t=5$$ and thus must be the right answer choice.
How did you solve this?

Incorrect.
[[snippet]]
If you plug in $$k=3$$, $$m=10$$, and $$t=5$$, then the goal you get is 2. However, for this answer choice is equal to
>$$m+k-t+2 = 10+3-5+2 = 10$$
This is not equal to 2. __POE__ this answer choice and move on.

Incorrect.
[[snippet]]
If you plug in $$k=3$$, $$m=10$$, and $$t=5$$, then the goal you get is 2. However, for this answer choice is equal to
>$$m+k-t+1 = 10+3-5+1 = 9$$
This is not equal to 2. __POE__ this answer choice and move on.

Incorrect.
[[snippet]]
If you plug in $$k=3$$, $$m=10$$, and $$t=5$$, then the goal you get is 2. However, for this answer choice is equal to
>$$k-m-t+2 = 3-10-5+2 $$
That's going to be negative and not equal to 2. __POE__ this answer choice and move on.

Incorrect.
[[snippet]]
If you plug in $$k=3$$, $$m=10$$, and $$t=5$$, then the goal you get is 2. However, for this answer choice is equal to
>$$k+t-m = 3+5-10 = 8-10=-2$$
This is not equal to 2. __POE__ this answer choice.

Be careful!
Questions will quickly become much more difficult and if you use algebra you will:
1. Greatly increase your chance of making mistakes.
2. Waste precious time.
So from now on, try to practice __Plugging In__—even for easy questions. That way you'll sharpen your __Plugging In__ skills for the really tough questions that will get you a high score.

Very good.

Correct.
[[snippet]]
Just pick some values for the variables. Try $$k=3$$, $$m=10$$, and $$t=5$$. Then rewrite the question with the values instead: *"If in 4 years from now, John will be 10 years old, then how old was John 4 years ago?"*
>*"If in 4 years from now, John will be 10 years old"*
This means he is currently 6 years old.
>*"how old was John 4 years ago?"*
If he is 6 now, then he was 2 years old 4 years ago. Since the answer to the question is 2, then 2 is your **goal value**.

$$m-k-t$$

$$m+k-t+2$$

$$m+k-t+1$$

$$k-m-t+2$$

$$k+t-m$$

I solved it by __Plugging In__.

I solved it using algebra.

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