Zenaida Is Asked to Add 428 and 686 in Vertical

Essay

Zenaida is asked to add 428 and 686 in vertical form. She begins by saying, "Six thousand plus four thousand..." The interviewer then asks her what column the six and four are in, and she identifies it as the hundreds column. She begins again by saying, "Four hundred plus six hundred is ten hundred," and writes 110 below the line. She then says we have to do tens. She does 20 plus 80 equals 100 and places that under the 110. She then adds 8 and 6 and writes 14 and then writes that below the 100. Adding, she says it is 224. Where does Zenaida go wrong? Discuss her place value understanding.