Numbers 3.1 has not replaced Numbers 2.3, nor the Dock icon that points to Numbers 2.3
Numbers 3 in in your Applications folder. Drag the icon to the Dock , right click and Options > Keep in Dock. Launch from there.
Numbers 2.3 is in a sub folder called iWork '09 inside the Applications folder. Both versions can run at once.
Numbers 2.3 on the left (3 column chart)
Numbers 3.1 on the right (4 column chart)