Final answer:
When a petrol tank is three-quarters full, it holds 20 liters more than when it's half full. The tank's total capacity is 80 liters, therefore at three-quarters full it holds 60 liters, compared to 40 liters at half full.
Step-by-step explanation:
To find out how much more petrol a tank holds when it's three-quarters full compared to when it's half full, we first need to establish the total capacity of the tank. We're told that when the tank is half full, it holds 40 liters. This means that the full capacity of the tank is 80 liters (since 40 liters represents half of it).
Next, to find out how much it holds when it's three-quarters full, we calculate three-quarters of the tank's total capacity:
¾ of 80 liters = 60 liters.
Finally, to determine how much more petrol it would hold at three-quarters full compared to half full, we subtract the amount it holds at half full from the amount when three-quarters full:
60 liters (three-quarters full) - 40 liters (half full) = 20 liters more.