Question 239782
three less than a product of two numbers?
Your statement would be: {{{3-xy}}}

one day the temperature dropped from -5 degrees f to -20 degrees f.  how many degrees did it drop?
In this case we take the final temperature and deduct the initial temperature.  Be careful with the negative signs.
The equation would be like this: 
Final - Initial = temperature change
(-20) - (-5) = ?
-20 + 5 = -15
The temperature dropped by 15 degrees.