Fahrenheit is Celsius - 32 then divided by 1.8 which is not an easy conversion luckily its also 9/5ths

The trick I found out was to subtract 32 from Fahrenheit then divide by 9 then multiply by 5.

The other trick, you subtract 10% from your Celsius times by 2, then add 32 but this one doesn't reverse well because you have to add 1/9th