We have rows of log, where each row has one more log than the level above.
We start with 15 at the top and end with 24 logs in the base.
So the total number of logs is the sum of the numbers 15, 16, 17,..., 24.
We can add:
15 + 24 = 39
16 + 23 = 39
17 + 22 = 39
18 + 21 = 39
19 + 20 = 39
We take the first and last row and add them, and get 39. If we do the same with the following rows, we see that the sum of logs is 5 times 39:
[tex]5\cdot39=195[/tex]There are 195 logs stacked.
