Estimating Square Roots
This applet helps you understand the mental math method of estimating square roots that is taught in my posts at Grey Matters called Estimating Square Roots and Estimating Square Roots: Tips & Tricks.
Any number from 0 to 999 can be chosen with the sliders, and you can use the checkboxes to see display or hide the method used to determine the numerator and denominator.
This method gives a quick mental square root estimate whose square is never farther from the given number than .25.
An online HTML5 version of this applet is available at:
http://geogebratube.org/material/show/id/14587