SOLUTION: A lorry tank was 3 / 5 full of petrol, 21 litres was then added and it is now 5 / 6 full. how many litres of petrol can the tank hold?

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Question 991887: A lorry tank was 3 / 5 full of petrol, 21 litres was then added and it is now 5 / 6 full. how many litres of petrol can the tank hold?
Answer by CubeyThePenguin(3113) About Me  (Show Source):
You can put this solution on YOUR website!
x = number of gallons the tank can hold when full

3x/5 + 21 = 5x/6
18x/30 + 21 = 25x/30

-7x/30 = -21

7x/30 = 21

7x = 21*30

x = 3 * 30 = 90