Here's the one that went viral, from the frustrated parent who claims - without much evidence - to have a BS in electronics engineering and extensive experience with differential equations and other higher math applications:

I, too, have had experience with differential equations - yuck! - but I don't need anything more than a basic understanding of subtraction to figure out what's going on. Here's the answer, in a nutshell: Jack got the wrong answer because he treated each of the small skips as representing the subtraction of 1 from the prior number. What he should have done was to treat each skip as representing the subtraction of 2 from the prior number until he got to 117, at which point he should have treated the last skip as representing the subtraction of 1 from the prior number, giving him the result 111, not 121.

Here is what is going on: the exercise is building on the fact that it is easier to subtract by simple numbers, such as 100, 2 or 1, than it is by a complicated number like 316. So, the idea behind the problem is this:

316 can be represented by its individual place values, like so: 300 + 10 + 6. It can also be represented as the following sum: 100 + 100 + 100 + 10 + 1 + 1 + 1 + 1 + 1 + 1. It can also be represented by this sum: 100 + 100 + 100 + 2 + 2 + 2 + 2 + 2 + 1. Using that information, you can work out the difference 427 - 316 like so: 427 - 100 - 100 - 100 - 2 - 2 - 2 - 2 - 2 - 1 = 111. It's a lot easier to subtract by 100s, 2s and 1s for little kids than it is to do the column subtraction right off the bat.

Again, I didn't need differential equations, I didn't even need algebra, all I needed was some basic information on the various ways of representing numbers using only 10 digits (0 to 9, inclusive), and addition.

Now, here is the criticism that should have been leveled at this question because, unless there is more context that we're not being given (a not unreasonable possibility, btw), it's too complicated, and strips the problem of its didactic strength, because it requires way too much figuring to come up with the values for those little skips. Instead, building off my discussion of the first problem, the first little skip should have represented the subtraction of 10 from 127, giving you 117. The next skip should have represented the subtraction of 5 from 117, giving you 112 - why 5? because 10 is too large here; we've already subtracted 100 + 100 + 100 + 10 = 310, so subtracting another 10 would give us 320, which is bigger than 316; that means we need to subtract a number smaller than 10 and the next logical number down is 5 - so we do the subtraction, and get 117 - 5 = 112. We then check to see how much we've subtracted by, and we see that we've only subtracted away 100 + 100 + 100 + 10 + 5 = 315, which means we still have more to subtract because 315 is less than 316. We consider another 5, but 315 + 5 = 320, which is too big - 320 > 316 - so we have to use a number smaller than 5. The next logical number down is 1, the easiest number of all to subtract by, and we know that we won't have to subtract more than 4 1s because we already know that subtracting 5 1s would be too much (because 5 1s = 5). We inspect what we've subtracted so far and we see that we've subtracted 315; we then check to see what happens if we subtract 1 from 112 by adding that 1 to 315 - if the result is too small we know we need to subtract more 1s). When we do this, we see that subtracting just one 1 gives us a total of 316, which is the number we have to subtract from 427. That means that our answer must be 112 - 1 = 111. And therefore that 427 - 316 = 111.

Had the problem been written this way, Jack's incorrect answer would have had to have been changed, perhaps to 106, on the basis that Jack subtracted two 10s, then one 1, on his number line.

Now, some may say that this is awfully complicated, but it's actually not. It's simplifying because it's breaking the problem down into a number of small steps each of which is very easy to do: subtracting 100 from a number three times, then a 10, then a 5 and finally a 1, is substantially easier than subtracting 316 all at once. The reason why it might seem complicated is because, again, the adult is viewing it from the adult perspective, where it's obvious how to do three-digit subtraction, and not from the perspective of a young kid who is trying to figure out how to do it in the first place at all.

This is a perfect example of what I said earlier about common core critics getting lost in the weeds and missing the real issues for which the common core materials should be criticized. "Frustrated parent" is criticizing the valid part of the question - breaking three-digit subtraction problems down into a set of simple steps - and completely missing the real problem with the problem (pun intended): the set of simple steps it uses is not at all intuitive based on what kids would most likely have learned to-date and requires so much trial and error to work it out that the didactic value of the question is missed altogether.