The two things are probably related. I’m the same way. You learn to compensate for a bad memory, for bad visualization techniques, for bad math skills, by adhering to certain routines and rules of thumb. Most people can easily remember, say, times tables. If you’re a dumbass, though, you’ll probably be forced to use some sort of mneumonic device or rule of thumb if you want to actually memorize them. Alternatively, you might just get really fast at going through every step to get the correct answer, kinda depends.