Addition and Subtraction - Efficient subtraction - Presentation

In Lesson 12 of the series on Efficient Subtraction, students are encouraged to explore various subtraction methods they have previously learned and determine which is the most efficient. The term 'efficient' is examined, prompting students to discuss its meaning in the context of mathematical operations. One activity presents the problem of subtracting 1,596 from 3,000, solved by three different students—Esin, Malachi, and Rosie—each using a distinct method: regrouping, subtraction as distance on a number line, and benchmarks, respectively. Students are then asked to identify which method is the most efficient, with the understanding that efficiency may vary based on individual comfort with the technique.

The lesson continues with a second activity where students are tasked with finding missing numbers in subtraction problems, applying the methods discussed to determine the most efficient approach. Additionally, the lesson poses a real-life scenario where Malachi has £1,200 and makes purchases, leaving students to calculate the remaining amount using three different methods. This practical application helps students understand the effectiveness of each method. The lesson concludes with an independent work section, where students use different methods to solve calculations and reflect on questions such as the efficiency of the column method, the effect of adjusting numbers when finding differences, and the circumstances where counting on is more efficient than using the column method. Alternative representations of subtraction, such as part-whole models or bar models, are also considered.