Q : 19        logs are stacked in the following manner: logs in the bottom row,   in the next row, in the row next to it and so on (see Fig. ). In how many rows are the  logs placed and how many logs are in the top row?

As, the rows are going up, the no of logs are decreasing,
We can clearly see that 20, 19, 18, ..., is an AP .
and here
Let suppose 200 logs are arranged in 'n' rows,
Then,

Now,
case (i) n = 25

But number of rows can not be in negative numbers
Therefore, we will reject the value n = 25

case (ii) n = 16

Therefore, the number of rows in which 200 logs are arranged is equal to 5

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