[{"_id":ObjectId("52cdef7c4bab8bd675297da5"),"name":"Technorati","number_of_employees":35,"offices":[{"description":"","address1":"360 Post St. Ste. 1100","address2":"","zip_code":"94108","city":"San Francisco","state_code":"CA","country_code":"USA","latitude":37.779558,"longitude":-122.393041}]}]

db.collection.aggregate([{"$match":{"offices.country_code":"USA"}},{"$addFields":{"numOfEmpPerOffice":{"$divide":["$number_of_employees",{"$size":"$offices"}]}}},{"$unwind":"$offices"},{$group:{_id:"$offices.state_code",totalEmp:{$sum:"$numOfEmpPerOffice"}}}])