The baking club realized they only have 2.7 kg of flour left from their original order. The only person to use the flour since they bought it was Sal who used .9 kg of flour to make cakes. Can you write an equation to solve for how much flour they had before Sal took some, and then solve that equation?
In this concept, you will learn to solve single variable subtraction equations.
Solving Single Variable Subtraction Equations
To solve an equation in which a number is subtracted from a variable, you can use addition to isolate the variable.
Let’s look at an example.
Here is another example.
Since the fractions have the same denominators you can add them together.
Earlier, you were given a problem about the baking club and Sal, who used their flour to make cakes.
They need to know how much flour they originally had so they can pay their supplier.
The club started with some flour, but Sal took .9 kg of this flour to make cake. They had 2.7 kg left. You have to find how much they had to begin with.
Use the addition property of equality and add .9 to both sides of the equation and solve.
The answer is they originally had 3.6 kg of flour.
Harry earned $19.50 this week. That is $6.50 less than he earned last week.
Next, solve the equation. Use the addition property of equality to add 6.50 to each side of the equation.
The answer is Harry earned $26.00 last week.
Solve each equation.
Use the addition property of equality and add 44 to both sides of the equation.
Use the addition property of equality and add 1.3 to both sides of the equation.
Solve each single-variable subtraction equation.
To see the Review answers, open this PDF file and look for section 7.8.