A kettle full of water is brought to a boil in a room with t

A kettle full of water is brought to a boil in a room with temperature 20°C. After 15 minutes the temperature of the water has decreased from 100° to 75°C. Find the temperature after another 13 min.

Illustrate by graphing the temperature function

Solution

After 15 minutes the temperature of the water has decreased from 100^o to 75^oC, which is by 100^oC-75^oC=25^oC.

After 1 minute the temperature of the water will decrease by 25/15 = 5/3 =1.67^oC.

The temperature after another 13 minutes will decrease by 13*(5/3) = 65/3 = 21.67^oC.

The temperature after another 13 minutes = 75^oC - 21.67^oC = 53.33^oC