Q. At which among the following temperatures, the indicator of Celsius and Fahrenheit thermometers will show the same reading?
Answer: -40°C
Notes: The formulas for converting between degree Celsius and degree Fahrenheit are: °F = (°C * 9/5) + 32 => °C = (°F - 32) * 5/9 To find the temperature when both are equal, we use an old algebra trick and just set ºF = ºC and solve one of the equations.
°C = (°C * 9/5) + 32
=>°C - (°C * 9/5) = 32
=>-4/5 * °C = 32
=>°C = -32 * 5/4
=>°C = -40
OR
°F = (°F * 9/5) + 32
=>°F - (°F * 9/5) = 32
=>-4/5 * °F = 32
=>°F = -32 * 5/4
=>°F = -40
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