db={"coll1":[{"_id":"abc","info":[{"user_status":true,"timeActive":2.0},{"user_status":false,"timeActive":1.0}]}]}

db.coll1.aggregate([{"$addFields":{"newField":{"$divide":[{$arrayElemAt:["$info.timeActive",0,]},{$arrayElemAt:["$info.timeActive",1,]}]}}}])