This video features the arithmetic operation of Subtraction represented by the sign (-). Just like addition, the utility of the number line is high in subtraction too. Initially subtraction in maths was done by the way of counting lines, or alternately dots. But not only is that a slow and time consuming process, but inconvenient for bigger numbers as well. Unlike the line method, the technique of the number line to subtract eases the process as well as boosts the visualizing ability of the child.
A differentiating factor in the use of number line for subtraction is that unlike in addition, where one only moves in the forward direction in the number line, in subtraction one has to move backwards after moving forward because units of a quantity are being decreased. Taking the example illustrated in the video, 5 – 2 means moving five places ahead in the number line and then two places backwards. The number obtained at the “resultant” steps is 3 which is the answer to the question.
Similarly, in 6 – 4, one first counts six places from zero on the number line and then counts four places backwards from that point. The number so obtained on the number line, i.e., 2 is the answer. 9 – 3 would be three places backward from the ninth place on the number line, resulting in 6. One can easily solve basic subtraction questions following this approach of the number line.