Question

Please, help worth as lot of points.

Answer 1

John has 135 baseball cards he gives his friend 64 how many does he have left?
It does have a solution the answer is 71

Tell him to avoid this very common error  where the student simply takes' the difference of the two digits in each column, irrespective of which is the larger. Doing this produces an error in which the student ought to borrow, but does not