$1$ heap of sand $+\ 1$ heap of sand $= 1$ heap of sand? My uncle, who barely passed elementary school math (which leads me to believe he read this in some kind of joke magazine), once told me this when I was very young. 
$$1 \text{ heap of sand } + 1\text{ heap of sand } = 1\text{ heap of sand}
.$$
It does sound like a joke, but as I learned more and more math (still at basic college math), I still couldn't (and can't) disprove/prove it. 
So we all know this is true "linguistically," since if you add 1 heap of sand to another one, it will still be a heap of sand, but mathematically, 1 + 1 cannot equal 1.
I expect there to be, and wouldn't be surprised if there weren't, similar questions to this one but I couldn't find it using the search feature.
I guess I'm going out on a limb here because of the stupidity (and perhaps the obvious answer) of this question, but I seriously cannot disprove this based on what I know. 

The issue is a misunderstanding of the words involved. One number plus one number is still one number; the numbers involved are not the same, but they're all numbers. Similarly, one heap of sand plus one heap of sand is another, completely different heap of sand. Being "a heap of sand" is a property, not an identifier. If you said "heap of sand A plus heap of sand A is heap of sand A", I would say no, that's false - adding "heap of sand A" to itself should duplicate each grain of sand, resulting in heap of sand B which is twice as large.
