Lesson 3.7: Alternate and student invented algorithms for addition and subtraction

Lecture:

Videos: Note, this time I have done each small piece separately (about 3 minutes per video), so if you want to go back and re-watch an algorithm, you can watch just one of the videos

Introduction

Teaching/Scaffolding algorithms

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

Student invented/mental math algorithms

Addition Subtraction Break both numbers into place value   Add on in chunks using place values of one addend Add up in chunks using multiples of ten as bridge numbers Add on in chunks using multiples of 10 as bridge numbers Take away in chunks using place values of the subtrahend   Place value and negative numbers Find friendly numbers and compensate at the end Ajust to friendly numbers (use place values for both) and compensate at the end. Make friendly numbers by compensating between addends Adjust to friendly numbers by changing both numbers to keep the same difference (shift the number line)

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

British standard way of writing addition Equal additions subtraction algorithm