why is a negative number subtracted by a whole number a larger negative number

If it is cold it will be a minus (or negative temperature).  Like if you are in a freezer!

So sometimes it helps if you think of negative numbes as being cold numbers and positive numbers as being hot numbers.

If you are already in the freezer (so it is a negative temperature) and you make it even colder (take away more heat ) then the temp will get even more negative

-5-6 (-5 take away 6 degrees of  heat = -11 degrees)

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WE REALLY NEED TO USE NUMBER LINES FOR THESE QUESTIONS!

Because the subtraction sign is actually a number's sign. For example, 2-3 can also be written as 2+(-3). and for adding two negatives, you could add the two numbers first, and then put a negative sign in, although that way will be more confusing. so I suggest to write as -x+(-y)=z.