1. Preheat oven to 350°F. Grease and flour 13×9-inch pan.
2. Combine cake mix, eggs, water and oil in large mixing bowl. Beat at medium speed with electric mixer for 2 minutes. Pour into prepared pan. Combine flour, sugar and baking powder in small bowl. Cut in butter until crumbly. Sprinkle evenly over batter. Bake at 350°F for 35 to 40 minutes or until toothpick inserted in center comes out clean. Cool completely in pan.
Butter or margarine will cut more easily into the flour mixture if it is chilled. Use two knives or a pastry cutter to cut the mixture into crumbs.