Answer:
After 15 minutes, the temperature of both the furnaces will be same.
Step-by-step explanation:
Let [tex]x[/tex] be the minutes when the temperature of both becomes same.
Now, as per question:
Temperature of the furnace after [tex]x[/tex] minutes that is cooling at the rate of 15 degree per minute is given as:
[tex]T=1200-15x[/tex]
Temperature of the furnace after [tex]x[/tex] minutes that is heating at the rate of 5 degree per minute is given as:
[tex]T=900+5x[/tex]
Now, equating both the temperatures, we get
[tex]1200-15x=900+5x\\1200-900=15x+5x\\300=20x\\x=\frac{300}{20}=15\ min[/tex]
Therefore, after 15 minutes, the temperature of both the furnaces will be same.