Try:
TWELVE SOLDIERS
+/-0.5 hours will cover it, but you're moving in the wrong direction relative to your previous answer.
New problem for MOU:
Twelve pacificists had to get to a place twenty-five miles distant with the quickest possible dispatch, and all had to arrive at exactly the same time. They requisitioned the services of a man with a small car.
"I can do ten miles an hour," he said, "but I cannot carry more than four men at a time. At what rate can you walk?"
"All of us can do a steady three miles an hour," they replied.
"Very well," exclaimed the driver, "then I will go ahead with four men, drop them somewhere on the road to walk, then return and pick up four more (who will be somewhere on the road), drop them also, and return for the last four. So all you have to do is keep walking while you are on your feet, and I will do the rest."
They started at noon. What was the exact time that they all arrived together