He is incorrect because any number multiplied by 1 will stay the same, and so if he is going to multiply it by numbers less than one, he will have a lower number.
For a linear system of equations, there can only be zero solution, 1 solution or an infinite number of solutions. Two lines cannot intersect more than once. The intersection of the lines is called the solution. For this case there could is no solution because it only shows one equation. It cannot intersect on its own line.
To solve this problem we can use proportion, but first its nice to transform our fraction into improper fraction, so

and

Now we can make proportion

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of fuel
x-----------------------------

Now we can cross multiply

- its the result
Divide
20/10 = 2
10*2 = 20
There are 2 wholes in 20/10
Answer: 2/1 or 2