Question

A thermometer reads 0${}^o$C as 10 ${}^o$C and 100${}^o$C as 90${}^o$C then
Find the correct temperature if the thermometer reads 20${}^o$C

• A. ${20}^o$C
• B. ${12.5}^o$C
• C. ${25}^o$C
• D. ${30}^o$C

Answer 1

The correct option is B ${12.5}^o$C

Temperature on any scale can be easily converted into different scale by the following formula

$\frac{T-T_f}{T_b-T_f}=\text{c}onstant$

where

$T$ = Reading of thermometer

$T_f$ = Freezing point of water

$T_b$ = Boiling Point of water

So here we will equate the reading of two scale namely, thermometer and actual scale.

$\frac{20-10}{90-10}=\frac{x-0}{100-0}$

$\frac{10}{80}=\frac{x}{100}$

$x={12.5}^{o}C$