Salesforce CEO Marc Benioff Business Insider Salesforce shares dipped as much as 10.7% on Wednesday after the company confirmed its $27.7 billion purchase of Slack and guided for its slowest revenue growth since 2009.The Slack deal's price tag reflects a 55% premium to where the firm's shares traded before news broke of the acquisition.Though Salesforce's third-quarter earnings beat estimates, its guidance for fourth-quarter revenue marked a weakening pace of year-over-year growth.Watch Salesforce trade live here.Salesforce slipped as much as 10.7% on Wednesday after confirming its acquisition of Slack and reporting soft forward guidance.The workspace-software company announced Tuesday afternoon it will buy Slack for $27.7 billion.