A galvanometer having a resistance of 20 Ω and 30 divisions on both sides has figure of merit 0.005 ampere/ division. The resistance that should be connected in series such that it can be used as a voltmeter upto 15 volt, is :
(1) 100 Ω
(2) 80 Ω
(3) 125 Ω
(4) 120 Ω
