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🤔 Which One Doesn't Belong?
Tap the item that doesn't belong with the others
Prime Numbers
Grade Level:
Elementary (4-5)
Middle School (6-7)
High School (8-9)
New Problem
5
7
61
21
Show Why
Mathematical Reasoning
This one doesn't belong because 21 is composite (has factors other than 1 and itself), while the others are prime.
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Multiple Rule
Equivalent Expressions
Prime Numbers
Composite Numbers
Expression vs Answer
Factor Rule
Parity Rule
Divisibility Rule
Perfect Power Rule
Equivalent Representations
True vs False Equations
Same Solution Rule
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