How many tenths are in a foot?

Ten tenths add up to one whole anything. Ten tenths of a foot are one foot. Same with ten tenths of a mile, an ounce, a century, a piano, a book, an Apple, and a city. If you divide something into parts and you have all of the parts, you have the whole thing.

If you mean something like "how many tenths of inches are in a foot," that's a different question. ---- You could change the measurement to the metric system, which is based on tenths.