Puzzle | Blow hot and blow cold

We know that 0°C is the same as 32°F. It is also a known fact that 100°C equals 212°F. But there is a temperature that gives the same reading on both Centigrade and Fahrenheit scales. Can you calculate this temperature?

Solution:

The formula which gives the relationship between Centigrade and Fahrenheit is:

F = 9/5*C + 32
To find the temperature which is same in both Centigrade and Fahrenheit scales. We have to find out the value of C or F by replacing C with F or F with C. By going through this idea we have a new equation from the above equation:
C = 9/5*C + 32
C – 9/5*C = 32
-4/5*C = 32

C = (-32*5)/4 = -40
F = 9/5*F + 32
F – 9/5*F = 32
-4/5*F = 32
F = (-32*5)/4 = -40

Now we can say that at -40 temperature both Centigrade and Fahrenheit scales are same.

Reference:http://www.physlink.com/education/askexperts/ae51.cfm