What is the common difference between successive terms in the sequence?9, 2.5, –4, –10.5, –17, ...

Subtract consecutive terms to find the common difference: 2.5 − 9 = −6.5. The next differences are also −4 − 2.5 = −6.5 and −10.5 − (−4) = −6.5, so the common difference is −6.5, choice B.

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