The answer is: [A]: " 4 and 5 " .
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Step-by-step explanation:
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Looking at the answers:
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we know that 4² = 16 ; and 5² = 25 ;
So: √16 = 4 ; and √25 = 5.
So: √21 must be between √16 and √25 ;
That is: √21 must be between 4 and 5 ; which is answer choice: [A] .
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