# Unit Conversion

1. Nov 15, 2014

### Foehammer

1. The problem statement, all variables and given/known data
A Celsius and a Fahrenheit thermometer are dipped in boiling water. The temperature of the water is brought down until the Fahrenheit thermometer reads 140°. So, the fall in temperature registered by Celsius scale is:
30
40
50
80

2. Relevant equations
F=(C*(9/5))+32
C=(F-32)*(5/9)

3. The attempt at a solution
Boiling water is 212 F. 212-140=72.
Convert 72 F to C and I get 22.223 C.
My answer doesn't match any of the choices.

2. Nov 15, 2014

### rock.freak667

If F=1.8C+32

Then F1=1.8C1+32
and F2=1.8C2+32

So you change in F, F2-F1= ? (write in terms of the formula and you'll see that the change in F can't be converted to C using the standard formula).

Alternatively, convert everything to C first.

3. Nov 15, 2014

### Foehammer

Got it. Thanks a lot!

4. Nov 15, 2014

### SteamKing

Staff Emeritus
The reason '32' appears in these temperature conversion formulas is that in the Celsius scale, water freezes at 0 C, while this occurs at 32 F on the Fahrenheit scale. Between freezing and boiling, there are 180 Fahrenheit degrees and 100 Celsius degrees, so each Celsius degree is 180/100, or 9/5 Fahrenheit degrees.