Subtração

Words to Math: Subtraction

In this section, we will learn to translate phrases into a mathematical expression by identifying key words that indicate subtraction.

When talking about subtraction, you will most likely see the terms "subtract", "less than", "minus", "difference", and "decreased by". There are different such terms for addition, multiplication, and division.

Let’s take a look at an example.

Sam has $6$ pencils. His friend, Jack, has $3$ pencils less than Sam. How many pencils does Jack have?

We know that the term "less than" often refers to subtraction, so the operator ‘$-$’ is required.

Since Sam has $6$ pencils and Jack had $3$ less than Sam, we can rewrite this as a mathematical expression.

Jack = Sam ($6$ Pencils) $-$ $3$ Pencils = $3$ Pencils

When talking about equality, you will most likely see the terms "equal to", "is", "the same as", and "amounts to".

Here are some phrases about subtraction translated into a mathematical expression.

1. $2$ less than $6$ is $4\quad\rightarrow\quad 6 - 2 =4$
2. $13$ minus $1$ equals to $12\quad\rightarrow\quad 13 - 1 = 12$
3. The difference between $10$ and $7$ is $3\quad\rightarrow\quad 10 - 7 =3$

This technique is useful for solving equations too. In that case, we're subtracting the same number from both sides of an equation.

We are now going to take a look at some of the types of problems you might encounter about subtraction word problems.

We know that the term "minus" refers to subtraction, so the operator ‘$-$’ is required.

The term "is" refers to equality, so the operator ‘$=$‘ can be used.

Replacing minus with ‘$-$’ and is with ‘$=$‘, we can rewrite the phrase given into a mathematical expression.

$15$ minus $8$ is $7\quad\rightarrow\quad 15-8=7$

We know that the term "less than" refers to subtraction, so the operator ‘$-$‘ is required.

Since Joey weighs $17$ pounds less than Nate who weighs $18$ pounds, we can rewrite this into a mathematical expression. $$\begin{align} &\text{Joey’s Weight } = \text{ Nate’s Weight }- 17\text{ pounds}\\ &\text{Joey’s Weight }= 185 - 17 = 168\\ &\text{Joey weighs }168\text{ pounds} \end{align}$$

Word Problems with Subtraction

The key to solving word problems is to translate them into mathematical expressions. This is made easier if you can pick out key phrases that tell you what type of operation the problem is asking for. We'll call these signal words.

(Video) Writing an Algebraic Expression from a Word Problem

by mrmaisonet

This video by mrmaisonet works through a few word problem examples with an identification of key words.

$\large{\text{Summary}}$

The problem he looks at is:

Katie has $12$ fewer dollars than Julia has. If $d$ equals the amount of money Julia has, write an expression for the amount of money Katie has.

Here $d$ is a variable. Our expression will have the variable in it somewhere. The key phrase is $12$ fewer. This means Katie has the same as Julia minus $12$. Therefore, we can say Katie has: $$d-12$$