Database
[{"_id":"50c4f4f2-68b5-4153-80db-de8fcf716902","name":"C156","posX":"-136350","posY":"-27350","posZ":"962","inspectionIsFailed":"False"},{"_id":"50c4f4f2-68b5-4153-80db-de8fcf716903","name":"C156","posX":"-136350","posY":"-27350","posZ":"962","inspectionIsFailed":"False"},{"_id":"50c4f4f2-68b5-4153-80db-de8fcf716904","name":"C156","posX":"-136350","posY":"-27350","posZ":"962","inspectionIsFailed":"True"}]
Query
db.collection.aggregate([{$group:{_id:null,totalCount:{$sum:1},failedCount:{$sum:{$cond:[{$eq:["$inspectionIsFailed","True"]},1,0]}}}},{$project:{_id:0,ratio:{$divide:["$failedCount","$totalCount"]}}}])