So, I understand that you one 1/10th, that is one tenth or [tex] \frac{1}{10} [/tex]
so:
[tex] \frac{1}{10} [/tex]*800=[tex] \frac{800}{10} [/tex]=80
The answer is 80.
I calculated this by dividing both the nominator and the denominator by the same number - this is always allowed. This number is 10.