TD Ameritrade's decision to take out a competitor in Scottrade makes sense, said TheStreet's Jim Cramer. TD Ameritrade said Monday that it entered into a "definitive agreement" to purchase online brokerage Scottrade Financial Services in a cash-and-stock deal valued at $4 billion. TD Ameritrade, the biggest discount brokerage by trade executions, said it expected to realize about $450 million in combined annual expense synergies, and more than $300 million in additional longer-term opportunities once the deal closes. Video provided by TheStreet