Double the number, then reduce by one-tenth the doubled number, then add 32

Example: To convert 25 C double it to 50, reduce by 5 to get 45, then add 32 to get 77 F.

The reason this works is because 9/5 = 10/5 - 1/5. And the nice thing about this is that it is an exact conversion not an estimation.

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I rarely care about the actual number. "Cold", "Not bad", "Warm", and "Hot" cover 99% of my weather related temperature interactions. I have also memorized 3 easy conversion points to estimate from if I care. If I really care...well I don't think that I ever have. Maybe cooking instructions, then I might care, but even that is usually just by feel. I'm not a baker.

10C = 50F 
28C = 82F
40C = 104F
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