When you divide a whole number by a decimal less than 1, the quotient is greater than the whole number. why?

Because division is repeated subtraction.

For example: "10 divided by 2" means "How many times can you
subtract 2 from 10 before the 10 is all gone ?".

When you divide a whole number by ' 1 ', you're trying to find out
how many times you can subtract ' 1 ' from the whole number. 
Of course, the answer is the whole number itself.

Now, when you divide a whole number by a piece less than ' 1 ',
you're trying to find out how many times you can take a piece of ' 1 '
away from the whole number.  Of course THAT will be more times
than the whole number itself.