Stephen went shopping to buy some new school supplies. He bought a backpack that cost $28.67 and a scientific calculator for $34.88. How much money did Stephen spend altogether?
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Guidance
To make the process of decimal addition simpler, you should add decimal numbers using the vertical alignment method. The decimal points must be kept directly under each other and the digits in the same place value must be kept in line with each other. If the decimal numbers are signed numbers, the rules for adding integers are applied to the problem.
Example A
Solution: Begin by writing the question using the vertical alignment method.
Don't forget that the decimal points must be kept directly under one another. To ensure that the digits are aligned correctly, add zeros to 48.6.
Add the numbers.
Example B
Solution: The first step is to write the problem using the vertical alignment method. The two decimal numbers that are being added have opposite signs. Apply the same rule that you used when adding integers that had opposite signs – subtract the numbers and use the sign of the number with the larger absolute value in the answer.
The number with the larger absolute value is 97.38 and it has a positive sign. This means that the sign of the answer will also be a positive value.
Example C
Solution: The first step is to write the problem using the vertical alignment method.
To ensure that the digits are aligned correctly, add zeros to 168.8.
Add the numbers.
The numbers being added each had negative signs. This means that the sign of the answer is also a negative value.
Concept Problem Revisited
Stephen went shopping to buy some new school supplies. He bought a backpack that cost $28.67 and a scientific calculator for $34.88.
Stephen bought two items. To determine the total amount of money he spent, add the prices of the items.
The numbers and the decimal points have been correctly aligned. Now add the numbers.
Stephen spent $63.55 altogether.
Guided Practice
1.
2.
3.
Answers:
1.You can add all three numbers at once.
2. Add the two positive numbers together:
Subtract the negative number from the result:
3.
Explore More
Add the following numbers.
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What is the cost of these items before tax is added?
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Jennifer bought the following school supplies:
 1000 sheets of paper  @$14.67
 36 pencils  @ $6.55
 1 binder  @$18.48
 1 backpack  @ $22.74
 1 lunch bag  @ $4.64
How much did Jennifer spend on these supplies before taxes?
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