help! i feel like im going crazy!
my brother and i were watching an anime when a temperature of 39.2°C came up. being american, we only understand Fahrenheit. so, for fun, we decided to see if we could convert it in our heads...
needless to say, we couldnt and ended up looking it up. regardless, later i kept trying to work it out on paper. i finally remembered how, but..... it keeps coming out 1 off??? where am i going wrong! help!!
Hi :D ngl i'm kind of obsessed with your notes, bc you wrote the whole multiplication process down and then checked your answer. anyway let's get right to it:
in your multiplication table for 39.2 * 1.8, the first row is 39.2*0.8=31.36 (correct), and then you did 39.2*1.0=40.20. somewhere you added an additional 1 even though when you write it down like 39.2*1.0 you can see that the 40.20 can't be right.
i hope that helped!
also if you wanna know a temperature in °F but you can deal with a rough estimate, here's what i usually do:
1.8 is almost 2, or, in other words, it is 2-0.2. it's way easier to double a number in your head than do the whole "multiply by 1.8 ... argh how did that work again, i need a pencil" shtick. for the sake of simplicity, let's say you want to know what 39°C are in °F, so you could
multiply by 2: that's 78. an easy way to do this in your head is by calculating 40*2 and then subtracting 2, because 39=40-1, so 39*2 = (40-1)*2=40*2-2
keep the 78 as a preliminary result in your mind. now, shift the decimal one place to the left: 78.0 -> 7.8
subtract these: 78-7.8 = 70.2
now add the 32 and there you got your rough estimate of 39.2°C -> 102.2°F
when you shift the decimal place one to the left (or, divide by 10), you essentially calculate the result of 39*0.2. you could sum up this whole calculation as
39*1.8+32 = (40-1)*(2-0.2)+32 = 40*2-2-(40*2-2)/10 = 78-7.8 = 70.2+32=102.2
-sorrel
