There are three uncharged identical metallic spheres 1,2 and 3 each of radius r and are placed at the vertices of an equilateral triangle of side d. A charged metallic sphere having charge q of same radius r is touched to sphere 1, after some time it is taken to the location of sphere 2 and is touched to it, then it is taken far away from spheres 1,2 and 3. After that the sphere 3 is grounded, the charge on sphere 3 is (neglect electrostatic induction by assuming d>> 2r)