How many stores with less need for products, and purchased through a distributor, are located in Washtenaw County?
less need for products refers to Order Quantity = 1; purchased through a distributor refers to Sales Channel = 'Distributor'; 'Harri County' is the County
SELECT SUM(CASE WHEN T1.`Order Quantity` = 1 AND T1.`Sales Channel` = 'Distributor' AND T2.County = 'Washtenaw County' THEN 1 ELSE 0 END) FROM `Sales Orders` AS T1 INNER JOIN `Store Locations` AS T2 ON T2.StoreID = T1._StoreID