Create and solve a linear equation by dragging the green circles up and down. The interactive graphics fill the whole screen so it is great for interactive whiteboards. Solutions must be natural numbers. From Yenka.com
http://www.yenka.com/freecontent/item.action?quick=lv#

These versions show if the equation is balanced or not, but the equation can't be changed.
http://www.yenka.com/freecontent/item.action?quick=lm#
http://www.yenka.com/freecontent/item.action?quick=ls#
http://www.yenka.com/freecontent/item.action?quick=lr#
http://www.yenka.com/freecontent/item.action?quick=ln#
http://www.yenka.com/freecontent/item.action?quick=lu#
http://www.yenka.com/freecontent/item.action?quick=lt#