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

db.collection.aggregate([{$facet:{result:[{$match:{}}],hr:[{$match:{name:"hr"}}]}},{$project:{result:{$map:{input:"$result",in:{$cond:[{$eq:["$$this.name","hr"]},"$$this",{name:{$concat:["$$this.name","/",{$first:"$hr.name"}]},value:{$divide:["$$this.value",{$first:"$hr.value"}]}}]}}}}},{$unwind:"$result"},{$project:{name:"$result.name",value:"$result.value"}}])