Sequence Word Problem General Question Whenever I do sequence word problems in my math homework I often end up accidentally adding 1 more term than needed, or subtracting 1 more term. Word problems seem ambiguous to me in wording a lot of the time and I don't know whether to do $(n-1)d$, or $nd$. Can anyone give some general guidelines as to when to use $(n-1)d$, or $nd$? I feel like I understand sequences well but once word problems come into play no matter how much practice I put in, I add or subtract a term extra.
Thank you.

An answer specific to the example in the comments: 
To find the difference between each row we can use the information about rows 3 and 12. We know that row three has 41 boxes, and row 12 has 23 boxes. Since we have an arithmetic progression, this means that 
$$
41+(12-3)n=23,
$$
or $n=-2$. Thus when you go up one row, you lose $2$ boxes. Note that we used $12-3=9$, because in going from row $3$ to row $12$ we moved upwards nine times. Even though there are 10 rows in this interval, we wish to keep track of the number of times we change rows. This I hope gets to the heart of your question. So now that we know $n=-2$, lets find the number of boxes in row $1$. Note that in going from row $3$ to row $1$, we move downwards twice. Thus our answer is $41+(1-3)*-2=45$.
A last piece of advice: when the number of rows or terms in your sequence is small, draw pictures! It is a great way to build intuition doing these problems,  and can be nice to check your work. 
Hope this helps!
