During Tim's addition, he might of had a carrying the number error.
7,846+5,683. First you add 6 and 3 which equals 9, then 4+8 which is 12, so you carry the one above 8 for your next adding problem. Then 8+6+1, which is 15, so you carry the 1 above the seven, so you add 7+5+1, which equals 13.The answer is 13,529.
I hope this helps.
