Mr kong earns $850 per month. He spents $500 and saves the rest. What is the ratio of the amount of money earned?

The amount of money saved is $850 - $500 = $<<850-500=350>>350.

The ratio of the amount of money earned is $350 : $500
Reducing the ratio to its simplest form, we get 7 : 10. Answer: \boxed{7:10}.