Skill: Write one-step equations from word problems

To write a one-step equation from a word problem:

1. Choose a variable for the unknown amount.
2. Describe what happens to that amount: Is something added, taken away, multiplied, or divided?
3. Write an equation that shows the two equal amounts.
4. Use the inverse operation to solve and check that the answer fits the story.

Example

Mia has some money. Her grandmother gives her $4.25, and now Mia has $11.75. How much money did Mia have at first?

1. Let $m$ represent the amount of money Mia had at first.
2. Mia’s original money is increased by $4.25, so the total is $m+4.25$.
3. The total is $11.75, so write:

$$m+4.25=11.75$$

4. Subtract $4.25 from both sides to undo the addition:

$$m=11.75-4.25$$ $$m=7.50$$

5. Check: If Mia started with $7.50 and received $4.25,

$$7.50+4.25=11.75$$

So, Mia had $7.50 at first.