(Reuters) - IT research and advisory company Gartner Inc IT.N said on Thursday it would buy CEB Inc CEB.N, a provider of business research and analysis, in a cash-and-stock deal valued at $2.6 billion to expand its business services.

The deal will broaden Gartner’s research business through the addition of CEB’s services, which include research and analysis related to human resources, sales, finance and law.

CEB’s shares were up 21.08 percent at $74.90 in afternoon trading, below the implied offer price of $77.25. They touched a high of $77 earlier. Gartner’s shares were down 9.2 percent at $92.47.

“They (Gartner) are buying a company that clearly has some issues in terms of slower growth... so it looks like the initial reaction isn’t favorable obviously like the management would have hoped,” BMO Capital analyst Jeffrey Silbert said.

On a conference call, Gartner CEO acknowledged CEB’s slower growth rate, but said he expected double digit growth for the combined company by the third year after close, likely in the first half of 2017.

Gartner said it would introduce CEB’s services for larger businesses to the mid-tier market, where Gartner has a greater presence.

Stamford, Connecticut based-Gartner is offering $54 in cash and 0.2284 of its shares for each CEB share. The offer represents a premium of about 25 percent to CEB’s Wednesday close.

Gartner shareholders will own about 91 percent of the combined company, which will house more than 13,000 associates serving clients in more than 100 countries.

CEB, headquartered in Arlington, Virginia, has a 35-day “go-shop” period during which it can solicit alternative proposals.

Gartner said the deal would immediately add to adjusted earnings per share on completion, and be “double-digit percentage accretive” to adjusted EPS in 2018.

Evercore and Goldman, Sachs & Co advised Gartner.

Centerview Partners LLC was lead adviser to CEB, with Allen & Co LLC also advising.