How do you know when to write zero in a quotient

The dividend (which is the first number that appears) will have zeros after the number put. For example, if you're dividing 4000 by 2 you're answer will have zeros at the end because their are zeros after the 4. You're answer will then be 2000

If the número has a zero in it then your quotient Will have zero too for example 1000x300=300,000