To do it without a calculator it would be easier to to find 1% to start (remembering 100%/100=1%). 100,000 /100 = 1000 then multiply this by 5 (to get the 5%) = 5000, this is the amount of to be added to the original sum. 100,000 + 5,000 = 105,000. Calculators are wonderful but it is useful to know exactly what you are trying to do then you can use the process in different situations. So, 33.33/100 = .03333 x 5=1.6665, 33.33+1.6665=34.9965. I hope this helps.