



 
Hi Geoff, If the mixture is 50 to 1 then 1 part in every 51 parts is oil. Thus the amount of oil in the 4 litre mixture is $\large \frac{1}{51} \normalsize \times 4 = 0.078$ liters which is 78 milliliters. Put that much oil in the tank and fill with gas to the 4 liter mark. Penny  


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