



 
Hi Don, Let me try a smaller example where I know the correct answer. You have an arithmetic sequence that starts with 3 and increases in steps of 4. Hence the sequence starts
Suppose the question is
You know the answer is 5 but how do you know that without writing them down? Think of the segment of the real line from 3 to 19. It is $19 3 = 16$ units long. If you walk along this line segment taking steps of length 4 units then you take $\large \frac{16}{4} \normalsize = 4$ steps, each footprint at the points of the sequence 3, 7, 11 and so on. Hence there are 4 steps after the footprint at 3 and hence there are $4 + 1 = 5$ footprints. Now try the original question. Harley  


Math Central is supported by the University of Regina and the Imperial Oil Foundation. 