For each sequence, decide whether it could be arithmetic, geometric, or neither.
25, 5, 1, . . .
25, 19, 13, . . .
4, 9, 16, . . .
50, 60, 70, . . .
\(\frac{1}{2},\) 3, 18, . . .
For each sequence that is neither arithmetic nor geometric, how can you change a single number to make it an arithmetic sequence? A geometric sequence?