Mathematics
Grade 7
15 min
Add and subtract decimals: word problems
Add and subtract decimals: word problems
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1
Introduction & Learning Objectives
Learning Objectives
Identify keywords in word problems that indicate addition or subtraction of decimals.
Translate real-world scenarios involving decimals into mathematical expressions.
Accurately add decimals, aligning decimal points correctly.
Accurately subtract decimals, aligning decimal points correctly and performing borrowing when necessary.
Solve multi-step word problems involving both addition and subtraction of decimals.
Estimate answers to decimal word problems to check for reasonableness.
Interpret the solution of a decimal word problem in the context of the original problem.
Ever wondered how much change you should get back at the store, or how much taller you've grown since last year? 📏 These are all situations where understanding decimals helps us sol...
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Key Concepts & Vocabulary
TermDefinitionExample
DecimalA number that includes a whole number part and a fractional part, separated by a decimal point.3.14 (where 3 is the whole number part and .14 is the fractional part)
SumThe result obtained when two or more numbers are added together. Often indicated by keywords like 'total,' 'altogether,' or 'in all.'The sum of 2.5 and 1.3 is 3.8.
DifferenceThe result obtained when one number is subtracted from another. Often indicated by keywords like 'how much more,' 'how much less,' 'remaining,' or 'left over.'The difference between 5.7 and 2.1 is 3.6.
KeywordsSpecific words or phrases in a word problem that provide clues about which mathematical operation (addition or subtraction) to use.'Total'...
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Core Formulas
Total Quantity Formula (Addition)
When a word problem asks for the total, combined, or 'in all' amount of several decimal values, you add them together.
This rule helps identify when to use addition. Look for keywords that imply combining quantities. Remember to align decimal points vertically before adding.
Remaining Quantity Formula (Subtraction)
When a word problem asks for how much is left, the difference, or how much more/less one quantity is than another, you subtract.
This rule helps identify when to use subtraction. Look for keywords that imply taking away, comparing, or finding a remainder. Align decimal points vertically and borrow when necessary.
Net Change Formula (Multi-Step Problems)
To find the final amount after a series of increases (addition...
5 more steps in this tutorial
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Challenging
Chen started the month with $250.45 in his checking account. He received a paycheck of $185.80 (a deposit). He then paid a phone bill of $62.75 and bought groceries for $95.30. Finally, he returned an item and got a refund of $15.50 (a deposit). What is his final account balance?
A.$278.20
B.$293.70
C.$192.20
D.$314.40
Challenging
Scenario 1: A container has 10.5 liters of juice. 2.75 liters are poured out, then 1.2 liters are added. Scenario 2: A different container starts with 12.0 liters of juice and 4.15 liters are poured out. What is the positive difference between the final amount of juice in Scenario 1 and Scenario 2?
A.0.90 liters
B.1.10 liters
C.0.80 liters
D.1.25 liters
Challenging
A wooden plank is 8.5 meters long. A carpenter cuts off two pieces. The first piece is 2.45 meters long and the second piece is 3.1 meters long. How much longer is the remaining piece of the plank than the first piece that was cut off?
A.0.50 meters
B.2.95 meters
C.0.40 meters
D.0.65 meters
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