A hot liquid takes 5 minutes to cool from 70°C to 60°C. How long will it take to cool from 60°C to 50°C ?

We know that rate of loss of heat c. temperature differencems(70−60)5∝70+602−T0∝65−T0and    ms(60−50)t∝60+502−T0∝55−T0This show that t should be greater than 5 minutes.