[{"name":"Alex","value":65},{"name":"petr","value":8},{"name":"hr","value":20}]

db.collection.aggregate([{$lookup:{from:"collection",pipeline:[{$match:{name:"hr"}},{$limit:1}],as:"hr"}},{$unwind:"$hr"},{$project:{doc:{$cond:[{$eq:["$name","hr"]},{name:"$name",value:"$value"},{name:{$concat:["$name","/","$hr.name"]},value:{$divide:["$value","$hr.value"]}}]}}},{$project:{name:"$doc.name",value:"$doc.value"}}])