3633. There are 10 ballpoint, 4 capillary and 2 helium pens in the box. On average, 10% of ballpoint, 3% of capillary and 0.5% helium pens are not written. Randomly taken pen writes. What is the probability that it is helium.

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