[{"key":1,time_zone:"Pacific Time (US & Canada)",verified:false,screen_name:"abc",friends_count:20,followers_count:100},{"key":2}]

db.collection.aggregate([{"$match":{"time_zone":"Pacific Time (US & Canada)","verified":false}},{"$project":{"screen_name":true,"FriendstoFollowersRatio":{"$divide":["$friends_count","$followers_count"]}}}])