The average temperature of 80° C and 50° C is 65° C, which is 45° C above the room temperature. Under these conditions, the body cools 30°C in 5 minutes. Using the equation.
we have \(\frac{30°C}{5min}\) = K (45° C) ……(1)
The average of 60° C and 30° C is 45° C which is 25° C above the room temperature. K is the same for this situation as the original.
Hence \(\frac{30°C}{t}\) = K (25° C) ……(2)
Divide (1) by (2), we get,
∴ Time taken = 9 minutes.
