Subtraction equations - 3 digit integers An equation is a mathematical statement such that the expression on the left side of the equals sign (=) has the same value as the expression on the right side. An example of an equation is - 200 - (- 600) = 400. One of the terms in an equation may not be know and needs to be determined. Often this unknown term is represented by a letter such as x. (e.g. - 200 + x = 400). The solution of an equation is finding the value of the unknown x. To find the value of x we can use the subtractive equation property which says: The two sides of an equation remain equal if the same number is subtracted from each side. We may also use the additive equation property which says: The two sides of an equation remain equal if the same number is added to each side. Example: x - (- 500) = 400 x + 500 = 400 x + 500 - 500 = 400 - 500 x + 0 = - 100 x = - 100 Check the answer by substituting the answer ( - 100) back into the equation. - 100 - ( - 500) = 400 Return to Top

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