What two numbers add up to 9990?

There are infinite combinations of two numbers that add up to 9990. Here are some examples using negative numbers:

-1 + 9991 = 9990
-2 + 9992 = 9990
-3 + 9993 = 9990
...

Here are some examples using two fractions that will add up to 9990:

9990/2 + 9990/2 = 9990
19980/3 + 9990/3 = 9990
29970/4 + 9990/4 = 9990
...

And here are some examples using two decimal numbers that will add up to 9990:

1.25 + 9988.75 = 9990
2.50 + 9987.5 = 9990
3.75 + 9986.25 = 9990
...

As you can see from the lists above, it can go on forever. However, when answering "What two numbers add up to 9990?", it may be more interesting to set some criteria to limit the result. We will set the follow criteria:

1) Only positive whole numbers can add up to 9990. (0 is not a positive or negative number and should not be included.)

2) Since a+b=29 is the same as b+a=29, we should only list it once.

Now, the answer to "What two numbers add up to 9990?" has 4995 answers:

1 + 9989 = 9990
2 + 9988 = 9990
3 + 9987 = 9990
.
.
4993 + 4997 = 9990
4994 + 4996 = 9990
4995 + 4995 = 9990

We have truncated the list above due to space, but you may be interested to know that we calculated the number of answers by dividing 9990 by 2 and then rounded down to the nearest whole number if necessary.

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