Grade 1 · Align ends to compare lengths · 307 of 750
Align ends to compare lengths: first strip length: 7 units; second strip length: 3 units
A design for a classroom activity uses strips of lengths 7 and 3 equal units. Find the longer strip and the difference between the lengths, explain the calculation, and check a related question.
Try the question, use a hint when you need one, and compare your reasoning with the worked solution. The animation starts with this chapter’s values; changing its controls explores a new case.
01 · Make a prediction
Your practice question
A design for a classroom activity uses strips of lengths 7 and 3 equal units. First find the longer strip and the difference between the lengths. Then answer: What extension would make the shorter strip exactly as long as the longer one?
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A starting point
Length comparisons require a common unit and aligned starting endpoints. A longer drawing caused only by a different display scale would not be a valid comparison.
Work through the reasoning
Step 1
Identify the quantities and the task
A design for a classroom activity uses strips of lengths 7 and 3 equal units. The first task is to find the longer strip and the difference between the lengths. Length comparisons require a common unit and aligned starting endpoints. A longer drawing caused only by a different display scale would not be a valid comparison.
Step 2
Calculate the original result
Length difference = |7 − 3| = 4. The longer strip reaches 7 units from the start; the shorter reaches 3 units.
Step 3
Complete the follow-up calculation
What extension would make the shorter strip exactly as long as the longer one? 4 units, because 3 + 4 = 7.
The answer
Length difference = |7 − 3| = 4. The longer strip reaches 7 units from the start; the shorter reaches 3 units. Follow-up: 4 units, because 3 + 4 = 7.
Compare the method as well as the result. A different valid method may reach the same answer. Keep exact values until the last step when the question asks for rounding.
02 · Explore the model
See the mathematical relationship move.
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Watch the relationship
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The mathematical idea
A design for a classroom activity uses strips of lengths 7 and 3 equal units. Length comparisons require a common unit and aligned starting endpoints. A longer drawing caused only by a different display scale would not be a valid comparison. The longer strip reaches 7 units from the start; the shorter reaches 3 units.
Length difference = |7 − 3| = 4
03 · Reflect and transfer
Explain what changes and why.
Trace both strips from their shared starting line. Compare the endpoints after both complete lengths are visible. Explain which quantity changes and which relationship stays valid. Use the starting values again before checking your written answer.
This is a distinct guided scenario using a reusable mathematical model. Similar-looking diagrams can represent different given values and conclusions; they are not different mathematical theories.