Substitution Method Word Problems

​Step #1: Identify the 2 totals.

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Now we are ready to apply these strategies to solve real world problems!

​Lets look at an Example:

​Mirna sold food at a soccer game to earn some extra money. She sold Pupusas for $2.00 and charamusca for $1.00, At the end of the match she made 15 dollars. She sold 10 pupusas and charamuscas combined. How many pupusas were sold and how many charamuscas were sold?

Lets start by identifying the important information:

• ​Pupusas cost $2

• ​Marachusca cost $1

• ​She sold 10 pupusas and marachuscas combined

• ​She made a total of $15

​Step 3: Determine the cost of each variable:

​P=$2

​M=$1

​Step 4: Write the first Equation: This first equation can represent the total number of food items sold.

​P + M =10

​Step 5: Write the second Equation: This second equation can represent the total number of money made.

​2P + 1M= $15

​Step 6: Write the equations so that the second is directly under the first and solve using your preferred method:

​P+M=10 P=10-M

​2P+1M=$15 2(10-M) + 1M=$15

​20-2M +1M =$15 -1M=-5 M=5 P+5= 10 P=5

• ​Step #1: Identify the 2 totals:

​In this case, we know the total number of coins and total cost.

Total number of Coins = 30

Total Cost = $4.80

• ​Step #2: Identify the variables.

What are the two items that you are comparing or trying to find?

Dimes = D

Quarters = Q

• ​Step #3: Determine the cost or amount of each item.

Since Dimes cost 25 cents and Quarters cost 25 cents, we can say:

Dimes = $0.10

Quarters = $0.25

• ​Step #4: Write the first equation.

We will start by writing an equation to show there are 30 coins. 

Since Lizzy only has dimes and quarters, our first equation will look like this:

D + Q = 30

• Step#5: Write the second equation.

We will then write an equation to show the total cost is $4.80. 

Since the cost of each dime is $0.10 and the cost of each quarter is $0.25, our second equation will look like this:

0.10D + 0.25Q = $4.80

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• Step#6: Rewrite the equations so that the second equation is directly under the first equation.

D + Q = 30

0.10D + 0.25Q = $4.80

Therefore, the system of equations for this scenario is:

D + Q = 30

0.10D + 0.25Q = 4.80.

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