Answer to Question #179800 in Algebra for Charity

Question

A learner subtract by using the vertical algorithm.

What calculation error did the learner make in subtraction

Answer 1

1. The calculation error made is that the learner borrowed from the 

hundred's column and not the ten's column. 

2. The conceptual error made is that the learner thinks that zero in the 

ten's column means there is nothing there. The learner does not 

realize that the zero has representation in this column as a tens place holder. He/she does not realize that when taking one of the hundreds 

from the hundreds column, he/she has now got ten tens in the tens 

column. 

3. The rule to “borrow from the next column” was not fully understood 

by the learner. If he/she understood he/she would not have made the 

error of borrowing from the hundred’s column and not from the ten’s 

when he/she is short of units in the units column. He/she has not 

realized that if there are no tens in the tens column (such as in this 

case) he/she does have to go to the hundreds column (which he/she 

did), but then that gives him/her ten tens in the tens column, from 

which he/she can borrow one ten to give him/her 13 units in the units 

column. 

4. The learner's existing knowledge is incomplete or inaccurate in this 

case. He/she is trying to follow the subtraction algorithm without 

fully understanding it.