The question is an illustration of arithmetic sequence.
<em>The number of conversation for 19 people is 171</em>
<u />
<u>(a) 9 people</u>
9 represents the number of people
8 represents the number of conversation each person had
2 represents the number of people having a conversation at once (i.e 2 people at once)
<u>(b) 19 people</u>
We have:
The number of conversation is:
So, we have:
Hence, the number of conversation for 19 people is 171
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