Describe and correct the error in evaluating the expression. 19-6+12-18=1
addition and subtraction are performed left-to-right. Since you have a result of 1, you must have subtracted 18 from 19. There is no way this could have been achieved using only + and - operations.
You could have done (19-(6+12))18 = 1
but that involves making many changes to a simple expression