In large bowl, beat cake mix, bananas, oil, water and eggs with electric mixer on low speed. Beat on medium speed 2 minutes, scraping bowl occasionally until smooth. Place 1 3/4 cups batter in 6-inch round pan. Spoon remaining batter into 16 lined muffin cups. Bake round cake 35 to 40 minutes and cupcakes 18 to 23 minutes or until toothpick inserted in cake comes out clean. Cool 10 minutes; remove from pans to cooling rack. Cool completely, about 30 minutes.