text: Propane\nC3H8 + 5O2 ---> 3CO2 + 4H2O\n\nTo work this out, assume compound is a hydrocarbon; atomic ratio is found by dividing % by atomic wt...\nC= 81.7/12 = 6.808\nH= 18.3/1.008 = 18.15\na ratio H/C of 18.15/6.808 = 2.666/1 or 8/3 in whole numbers...thus  C3H8\n\nSuccess!...had this simple try not worked out, some combo containing O, N or other atoms would have been necessary.