?x 0 goes to 0 in the ones place
? x 1 goes to the other factor in the ones place
? x 2 goes to 0,2,4,6 or 8 in the ones place
? x 5 goes to 0 or 5 in the ones place
? x 9 goes to 1 less than the unknown factor in the tens place
9.5m questions
12.2m answers