Leila says that 75% of a number will always be greater than 50% of any other number.

That is not correct, it depends on the numbers you are referring to. For instance, 75% of 100 is 75, but 50% of 1000 is 500, so in this case the 50% of a number is higher than 75% of another number. Although, is true that 75% is higher than 50% of the same number always.