4255. In two identical boxes are the pencil "Designer". It is known that 0.4 pencils in the first box and 0.3 in the second are characterized by TM hardness. At random, one box is selected and one pencil is drawn at random from it. It turned out to be hardness tm. What is the probability that he is out of the first box.

Detailed solution. Decorated in Microsoft Word 2003 (Quest decided to use the formula editor)