There are 100 parts in the box, of which 30 are 1st grade parts, 50 are 2nd grade, the rest are 3rd grade. How many ways are there to extract one part of the 1st or 2nd grade from the box
A part of the 1st grade can be extracted in n1 = 30 ways, the 2nd grade – n2 = 50 ways. According to the sum rule, there are N = n1 + n2 = 30 + 50 = 80 ways to extract one part of the 1st or 2nd grade.
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