1188. When stamping 70% of the details come out first grade, 20% - the second, 10% - the third. Determine how many stamped parts should be taken so that, with a probability of 0.9973, it could be argued that the frequency of appearance of first-class ones among them will differ from the probability of producing a first-class detail in absolute value by no more than 0.05.

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