Answer:
3 and 4
Explanation:
Powers, roots, and logs are monotonically increasing functions of increasing positive numbers. So, square roots are in the same order as squares. 3^2 < 11 < 4^2, so 3 < √11 < 4.
√11 is between 3 and 4.
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Additional comment
You may find it helpful to memorize square numbers up to about 20².
Your calculator can tell you √11 ≈ 3.317, a number between 3 and 4.