Hot water cools from 60oC to 50oC in the first 10 minutes and to 42oC in the next 10 minutes. The temperature of the surrounding is

According to Newton's law of cooling,              θ1−θ2t=Kθ1+θ22−θ0In the first case, (60−50)10=K60+502−θ0   1=K(55−θ0)     ………..(i)In the second case (50−42)10=K50+422−θ0     0.8=K46−θ0 ………(ii)Dividing (i) by (ii), we get 10.8=55−θ46−θor  46−θ0=44−0.8θ0⇒θ0=10∘C