其它
There are seven people in a bus. Four passengers get on and $6$ passengers get off at the first station. Then seven passengers get on and three get off at the second station. How many passengers are there on the bus at this time? 
Overseas Competition->Knowledge Point->Calculation Modules->Whole Numbers->Whole Numbers Addition and Subtraction ->Addition and Subtraction of Whole Numbers
$7+4-6+7-3=9$ 