The Dead Sea is ten times saltier than the ocean.
Why it is true
With a salinity of about thirty-four percent, it is nearly impossible to sink in its extremely dense waters.
Source: NOAA
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.