Mr. A, you are making too much of this. Sometimes you actually have to do some work. You don't have to do it in your head. Use a piece of paper or a calculator.
If I buy one 34-cent stamp, I have 2.9 - 0.34 = 2.56. Well, I do think most people can look at that and tell 256 is NOT a multiple of 20.
So, let's go the other way. Multiples of 20 allllllll end in 0 - 20, 40, 60, etc. What can I multiply 34 by to get a product that ends in 0 and subtracts from 290 resulting in a multiple of 20? You don't need to do it in your head. Grab your calculator and start.
2.9 - 0.34(1) = 2.56. Well, again, I can tell 2.56 is not a multiple of 20.
Back up a couple of spaces and change the 1 to a 2. Keeeeeep going . You don't even need your parameters (though nice work) because eventually you'll end up with a negative answer if you don't recognize your multiples of 20.
Yeah, you could start with 2.9 - 0.2(1), but most people know their multiples of 20 better than 34.
Go for it.
Mr A.
Non-negative integer? I think I understand that it can't exceed parameters where (x = 8.5, y = 0) and (x = 0, y = 14.5). Thus, the numbers can't be negative -- where 'x' or 'y' are less than '0' -- nor can't exceed 8.5 and 14.5. I am not quite sure whether I had to list all these possibilities in order to find the correct answer. Is there another way, perhaps a shorter way, that doesn't require me to make a list or chart to guess from, is what I am wondering? Looking at the possibilities x = 5, y = 6 seems pertinent. However, it took me too long to figure out this problem.07/06/19