Question #5ec5e

1 Answer
Feb 27, 2017

Temp.after9mins#=269°C#, total time#31.625 # minutes #31'37.5''#

Explanation:

First 3 minutes#=-23 xx 3=-69°C#

Next 15 minutes#=-15 xx 15=-225°C#

Total cooling after 18 minutes#=-225-69=-294°C#

#:.428°C-294°C=134°C#

#:.134°C-25°C=109°C# needed to cool down to 25°C

after 15 minutes#=-8°C # for # x # minutes to reach 25°C

#:.8x=109#

#:.x=109/8#

#:.x=13.625# minutes

#13.625 xx -8=109#

#:.3+15+13.625=31.625# minutes in total to cool down to room tempreture 25°C

#.625 xx 60= 37.5# seconds