[{"grades":[{"grade":"A","score":2},{"grade":"A","score":6}],"name":"Morris Park Bake Shop","restaurant_id":"30075445"},{"grades":[{"grade":"A","score":8},{"grade":"B","score":23}],"name":"Wendy'S","restaurant_id":"30112340"},{"grades":[{"grade":"A","score":2},{"grade":"A","score":11}],"name":"Dj Reynolds Pub And Restaurant","restaurant_id":"30191841"}]

db.collection.find({$expr:{$gt:[{"$avg":"$grades.score"},5]}},{average_socre:{$avg:"$grades.score"}})