there are several methods to accomplish subtraction. the method which in the united states is referred to as traditional mathematics teaches elementary school students to subtract using methods suitable for hand calculation. the particular method used varies from country to country, and within a country, different methods are in fashion at different times. reform mathematics is distinguished generally by the lack of preference for any specific technique, replaced by guiding 2nd-grade students to invent their own methods of computation, such as using properties of negative numbers in the case of terc.