The resistance of a resistance thermometer has values  2.7Ω and  3.7Ω at 00C and 1000C respectively. The temperature at which the resistance is 3.1Ω  is

Rt, R0,  R100, are resistances of wire at t0C,00C,1000C then temperature is t=Rt−R0R100−R0×100 substitute the given values in above equation t=3.1−2.73.7−2.7×100 ⇒t=0.41×100 ⇒t=400C