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Quick instructions If your browser is not JavaScript capable you can display the applet clicking on the link: THE APPLET Each of the four white rectangles in the panel of this applet represents one unit. A selection of a number from the upper choice box divides the upper wide rectangle into that number of equal parts. Clicking on the upper "DIV" button changes its label to "FRA" and allows you to select a certain number of the consecutive equal parts. This selection is done by clicking on one of the parts there. Then all preceding parts and the part clicked upon are colored (cyan). These colored parts constitute a certain fraction of the whole unit. Simultaneously this fraction is formally recorded on the small blackboard. If the selected fraction can be simplified (reduced), the simplified notation of it is also displayed. The same way another fraction in the lower vide rectangle can be constructed. Its color will be light green. If you want to change the selected fractions just click on another part of selected rectangle. To change current partition click on the proper "FRA" button and make a new selection. If you are satisfied with your selection of fractions click on the "SET" button that frozes the selected fractions and enables the choice of the least common denominator for the selected fractions. Correct choice of it divides the parts in both rectangles into smaller and common for both rectangles parts. On a top of it this the new parts must be the biggest possible. Only if these conditions are fulfilled the operation button "+/-" is activated. During the selection of the least common denominator the selected partition is shown in both narrow rectangles. This allows you to see how this partition fits to the partitions previously selected for the wide rectangles. When the "+/-" button is activated, select if you want to add or subtract the fractions. The first click on it selects addition and later on you can toggle between the subtraction and addition as long as none of the wide rectangles is clicked upon. Such click selects operation (addition or subtraction) and creates the original fractions in the narrow rectangles with their formal descriptions on the two additional small blackboards. It also partitions the original fractions in the wide rectangles in accordance with the selected common denominator. Keeping the button mouse down on the one of the colored parts of any wide rectangle may cause temporary disapearence of this and all following colored parts. Now these parts are ready to be moved to the other rectangle. If addition is selected, the mouse cursor should be dragged to the first white partition in the other rectangle and the mouse button realised there. Then the parts that dissapeared in the first rectangle will show in the other rectangle. When one of the rectangles is totally filled, the addition process is finalized and you can analyse its graphics results. The formal results are shown on the two adjacent blackboards. In the case of subtraction, the mouse cursor should be realised over such colored part of the other wide rectangle as you would try to remove the some number of colored parts from there as you already have removed from the first rectangle. If everything is done correctly they will indeed disapear. Thus the subtraction process of the colored parts of the lower rectangle from the colored parts of the upper rectangle will be partially executed. Now you can repeat this process again. As soon as one of the rectangles does not have any colored parts, the subtraction process is finalized. If some colored parts are left only in the upper rectangle, the final result is positive. Otherwise it is negative or zero (if nowhere the colored parts are left). The formal results of the performed operations are shown again on two adjacent small blackboards. To start a new problem of fraction addition or subtraction use the "RESET" button at any time.
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