Summary List PlacementWhen dating-app Bumble goes public this week, it will mark a significant milestone for investment giant The Blackstone Group. A relatively new unit of the world's largest private-equity firm has played a key role in the maturation of the dating app, which plans to go public on Thursday and is targeting a $1.8 billion IPO and a valuation of more than $7 billion, according to an updated S-1 filing on Monday.