human
Recognise and use efficient strategies for mental subtraction Jo and Paul are discussing mental addition and subtraction strategies.

Jo says a good way to add \( 19 \) is to add \( 10 \), then another \( 10 \) and then subtract \( 1 \).

Paul says a good way to subtract \( 19 \) is to subtract \( 10 \), then another \( 10 \) and then add \( 1 \).

Who is correct? Only
Jo
gpt
Does not understand the effect of consecutive operations