Lesson 3.4: Alternate and student invented algorithms for addition and subtraction

Lecture: Text

Videos: Note, this time I have done each small piece separately), so if you want to go back and re-watch an algorithm, you can watch just one of the videos

Introduction

Student invented/mental math algorithms

Addition Subtraction Adding on in chunks using multiples of 10 and 100 as bridge numbers Adding up to the minuend in chunks using multiples of 10 (and 100) as bridge numbers Add in place values and combine Subtract in place values using negative numbers, the negative numbers algorithm Add highest place values and compensate Subtract highest place values and compensate   Shift the number line

Teaching/Scaffolding algorithms

Expanded addition Break into place values (expanded subtraction)   Trade first subtraction

Algorithms that are standard in other countries and/or used to be common here

British standard way of writing addition Equal additions subtraction algorithm