Question

Erica used friendly numbers to find 43-19. She added 1 to 19 and subtracted 1 from 43. What is Erica's error?

Answer 1

I think that it is....
42-20=22

Answer 2

She could have added 1 to 19 to give 20 then subtracted  this from 43 to give 23. Then she can add the 1 to 23 to get the correct answer which is 24.