A department store buys a batch of toothbrushes at a wholesale price of 3.5 yuan each, and a retail price of 4 yuan each. When the remaining 200 toothbrushes are sold, calculate the selling price. In addition to the cost of all the purchases, a profit of 1,000 has been made Yuan, how many toothbrushes are bought in the store?
百货商店按批发价买进一批牙刷，每支3.5元，零售价每支4元，当卖到剩下200支时，计算卖得的钱，除去全部买进的成本外，已获利1000元，问商店买进牙刷多少支？
<gadget id="calculator">4 * 200</gadget>
<output>800</output>

<gadget id="calculator">1_000 + 800</gadget>
<output>1_800</output>

<gadget id="calculator">4 - 3.5</gadget>
<output>0.5</output>

<gadget id="calculator">1_800 / 0.5</gadget>
<output>3_600</output>

<result>3_600</result>