请教prep 数学

For a finite sequence of nonzero numbers, the number of variations in sign is defineded as the number of pairs of consecutive terms of the sequence for which the product of the two consecutive terms in negative. What is the number of variations in sign for the sequence 1 -3 2  -4 -6

DS: On her way home from work, Janet drives through several tollbooths. Is there a pair of these tollbooths that are less than 10 miles apart?

1 The first tollbooth and the last tollbooth are 25 miles apart

2 Janet drives through 4 tollbooths on her way home from work

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