OpenStudy (anonymous):

Logs are stacked in a pile. The top row has 15 logs and the bottom row has 24 logs. How many logs are there in the stack?

5 years ago
OpenStudy (jim_thompson5910):

You can do it the long way 15+16+17+18+19+20+21+22+23+24 OR You can use the formula S = (n*(first term + last term))/2 Where n is the number of terms

5 years ago
OpenStudy (anonymous):

Do we just assume that each succeeding stack will have 1 log less that the previous one (starting from bottom n going upward) ????

5 years ago
OpenStudy (jim_thompson5910):

yes, I'm assuming that the log stack is a pyramid

5 years ago
OpenStudy (jim_thompson5910):

|dw:1341347491683:dw|

5 years ago
OpenStudy (jim_thompson5910):

lol something like that

5 years ago
OpenStudy (anonymous):

But this assumption is not supported by any fact from the question.....

5 years ago
OpenStudy (jim_thompson5910):

true, but you can imagine stacking logs like that, so I don't see why not

5 years ago
OpenStudy (jim_thompson5910):

hopefully the picture I drew makes sense

5 years ago
OpenStudy (anonymous):

Yeah, that way it works out but I guess there must be another way without this assumption... Anyone with any other solution???

5 years ago
OpenStudy (jim_thompson5910):

hmm how else would you stack it? You can't exactly stack one log on top of the other (without support from another log). Besides, the number of logs decreases as you go up, so that's mostly why I made that assumption.

5 years ago
OpenStudy (anonymous):

I know that intuitively this is right but.........???

5 years ago
OpenStudy (jim_thompson5910):

good point, they might use other means to stack it...but I'm still sticking to my original answer

5 years ago