There are many English words that you can add an “s” to make it plural. But far fewer words become singular when you add an “s”. What are two examples of these much rarer words?
When Julian and Penelope met, one was half the others age plus seven years. Ten years later when they married, Penelope was thirty, but this time one was nine tenths the age of the other. How old was Julian? (No fractions or partial years, whole numbers only).
You are decorating for spring and you’ve found a bargain. A huge box of beautifully decorated tiles, enough to provide a border in two rooms. You really can’t figure out how to arrange them. If you set a border of two tiles all around, there’s one left over. If you set three tiles all around or four or five or six there’s still one tile left over. Finally you try a block of seven tiles for each corner and you come out even. What is the smallest number of tiles you could have to get this result?