Online College Courses for Credit

Left-to-right subtraction algorithm

Left-to-right subtraction algorithm

Author: Christopher Danielson

To help the reader perform the steps of the left-to-right subtraction algorithm for multi-digit numbers, and to suggest some productive ways of thinking about addition in the process.

See More

Try Our College Algebra Course. For FREE.

Sophia’s self-paced online courses are a great way to save time and money as you earn credits eligible for transfer to many different colleges and universities.*

Begin Free Trial
No credit card required

46 Sophia partners guarantee credit transfer.

299 Institutions have accepted or given pre-approval for credit transfer.

* The American Council on Education's College Credit Recommendation Service (ACE Credit®) has evaluated and recommended college credit for 33 of Sophia’s online courses. Many different colleges and universities consider ACE CREDIT recommendations in determining the applicability to their course and degree programs.



The left-to-right algorithm for subtracting multi-digit numbers feels highly unusual to most people when they learn it for the first time (especially to adults). This packet demonstrates the algorithm, and it suggests that there are some important connections between this algorithm and the ways people think about numbers.

Example 1: No regrouping

This video demonstrates the basic algorithm and demonstrates its relationship to (1) the standard algorithm for subtracting multi-digit numbers, and (2) ways of thinking about subtracting multi-digit numbers.

Example 2: Regrouping

This video demonstrates what happens when we need to regroup in the left-to-right algorithm.

Example 3: Regrouping twice

This video demonstrates multiple regroupings.

Example 4: A difficult computation