From Sherry, middle school student. Dear sir or madam, Question: how do I calculate the correct fuel ratio for a boat motor? 50:1 the oil containers only say how many ounces to add to 5 gallons of fuel to make a 50:1 ratio.(13 ounces to 5 gallons of fuel) I have a 20 gallon tank so what if I add 11.6 gallons of fuel, what formula would I apply to get the correct measurement of oil to add? could you explain it so that my dad could understand it? (like tell him exactly what do on the calculator) Thank you, Sherry Hi Sherry, There are 4 quarts in a gallon and 2 pints in a quart, hence there are 4 x 2 = 8 pints in a gallon. Each pint is 16 ounces so there are 8 x 16 = 128 ounces in a gallon. Hence the 11.6 gallons that you want to add is 11.6 x 128 = 1484.8 ounces. Now think about adding the gas and oil a little at a time. 50 ounces of gas and 1 ounce of oil. 50 ounces of gas and 1 ounce of oil. 50 ounces of gas and 1 ounce of oil. 50 ounces of gas and 1 ounce of oil. . . . Thus in each step you add 51 ounces of fuel (50 ounces of gas and 1 ounce of oil). Since you want 1484.8 ounces in total you need to do this  1484.8/51 = 29 times. Hence you add 29 ounces of oil and 50 x 29 = 1450 ounces of gas. This is 1450 + 29 = 1479 ounces or  1479/128 = 11.5 gallons of fuel. Cheers, Penny Go to Math Central