Certain quantity of water cools from 70°C to 60°C in the first 5 minutes and to 54 °C in the next 5 minutes. The temperature of the surroundings is:

By newton's law of coolingθ1-θ2t=kθ1+θ22-θ0 ⇒   70-605=k70+602-θ0 ⇒              2=k65-θ0               ..(i) and         60-545=k 60+542-θ0 ⇒         65=k57-θ0                  ..(ii)By dividing eqn.(i) by eqn.(ii) we have 106=65-θ057-θ0⇒θ0=45o