Fahrenheit
F = 9/5C + 32 doesn’t work for you
Subtract the first digit of the result from the result and add 32. It works pretty well; you’re usually right on but you’ll never be more than 1 degree Fahrenheit off.
For example, 23 C equals 74 F.
23 C x 2 = 46;
46 – 4 = 42;
42 + 32 = 74 F
or (an actual temp during a Christmas visit in Kruger)
42 C x 2 = 84;
84 – 8 = 76;
76 + 32 = 108 F and hot