Answer:
The number that gives the same result if it is multiplied by 999/998 or if any number is added to it is zero (0).
The property of a number being unchanged after being multiplied by a fraction and a constant is called an "Identity element". The identity element for multiplication is 1 and for addition is 0.
When any number is multiplied by 1, it stays the same. So, if we multiply any number by 999/998, which is equivalent to multiplying by 1, it stays the same.
Similarly, when any number is added to zero, it stays the same. So, if we add any number to 0, it stays the same.
Therefore, the only number that gives the same result if it is multiplied by 999/998 or if any number is added to it is zero (0).