Out of a group of 100 patients being treated for chronic back trouble, 25% are chosen at random to receive a new, experimental treatment as opposed to the more usual muscle relaxant-based therapy which the remaining patients receive. Preliminary studies suggest that the probability of a cure with the standard treatment is 0.3, while the probability of a cure from the new treatment is 0.6. Sometime later, one of the patients returns to thank the staff for her complete recovery.

”What is the probability that she was given the new treatment?”

  1. 0.375
  2. 0.425
  3. 0.4
  4. 0.525