An unknown resistance R 1 is connected in series

with a resistance 10 ohm. This combination is

connected to one gap of a metre bridge while

the other gap is connected to another resistance

R 2 . The balance point is at 50 cm. Now, when

the 10 ohm resistance is removed, the balance

point shifts to 40 cm. Then the value of R 1 (in

ohm) is

(a) 60

(b) 40

(c) 20

 (d) 10.