2/3 + 1/6 = 4/6 + 1/6 = 5/6...so he sold 5/6 of his hotdogs
5/6(200) = 1000/6 = 166.6 rounds to 167...so he sold 167 hotdogs
200 - 167 = 33 left
or, u can do it this way...
if he sold 5/6 of his hotdogs, then he has 1/6 left
1/6(200) = 200/6 = 33.33 rounds to 33 left