Arlette set her watch 5 seconds behind, and it falls behind another 1 second every day. How

many days has it been since Arlette last set her watch if the watch is 29 seconds behind?

So we know that it's already 5 seconds behind on the first day.

On the second day, it's 6 seconds behind.

And on the third, it's 7 seconds behind.

And so on ...

The difference between the day, and the seconds is 4.

This means, that whatever day it is (say 17 for example), and add 4, will come to how many seconds behind (17 + 4 = 21 in this case) !

So we subtract 29 by 4, to find the day:

29 - 4 = 25 days.