The effective capacitance of two capacitors of capacitances C1' and C2' (with C2′>C1′) connected in parallel is 25/6 times the effective capacitance when they are connected in series. The ratio C2′C1′ is :

C1′+C2′=256C1′C2′C1′+C2′ ⇒       6C1′+C2′2=25C1′C2′ ⇒6C1′2+6C2′2−13C1′C2′=0         ...(1) Let                C2′=xC1′ eqn. (1) becomes 6x2−13x+6=0                                                x=3/2 or 23 Since C2′>C1′           x=23 is not possible.