Final answer:
Ian should add 0.1 gallons of oil to the tank.
Step-by-step explanation:
According to the given ratio of gasoline to oil (40:1), Ian should add 3 gallons of gasoline to every 1/40th of a gallon of oil. To determine the amount of oil Ian should add, we divide 3 gallons by 40.
When we divide 3 by 40, we get the result of 0.075 gallons of oil.
To round this to the nearest tenth, we can consider the digit in the hundredth place, which is 7. Since 7 is greater than or equal to 5, we round up to the next tenth. Therefore, Ian should add 0.1 gallons of oil to the tank.
In summary, Ian should add 0.1 gallons of oil to the tank based on the given ratio of 40:1 for gasoline to oil.