SOLUTION: A 12-wheeler truck is loaded with 13 piles of log. The bottom row contains 25 logs. Each of the remaining piles contains 2 logs less than the number of logs on a pile directly belo

You have two ways.


First way is to notice that the numbers are

   25 logs   (1-st, bottom pile)

   23 logs   (2-nd, next pile)

   21 logs   (3-rd pile)

   19 logs

   . . . . . 

   25-2*(13-1) = 25-2*12 = 25-24 = 1 log (13-th pile)


Then to add the numbers 25 + 23 + 21 + 19 + . . . + 1  manually or using your calculator.


For it, there is no need to watch YouTube videos, at all.



But if you know what an arithmetic progression is, you may apply formulas for summing its terms.


You have 13 terms; the first term is   = 25;  the last, 13-th term is   = 1.


Hence, the sum of the thirteen terms is   =  =  =  = 13*13 = 169.   


The last step is to multiply 57 kilograms by 169.