Which fallacy is this? Assume that all people are either right-handed or left-handed, and likewise either right-footed or left-footed. 90% of people are right-handed. 90% of right-handed people are right-footed, but only 50% of left-handed people are left-footed as well. Which is more common: left-handedness or left-footedness?
STOP here, and have a go at answering that question first before continuing.
And then read on:
The answer is easy enough to get if you calculate it. Yet it feels counter-intuitive. Two people I tested this on (another used maths and got it right) assumed that because right-footedness is so dominant among right-handers and common among left-handers, that right-footedness should be even more common than right-handedness. There's some sort of fallacy at work here: any idea of what it is?

https://en.wikipedia.org/wiki/Prosecutor's_fallacy
People will see that half of the the left handed people are left footed and assume that left handed people are more common, but they don't realize that a small set of a large population can be comparable to a large set of a small population.
