# Thread: Rather basic conversion formula.

1. ## Rather basic conversion formula.

Hey all. Good to be here. Do need some random conversion help, shouldn't be particularly difficult.

Basically I want to convert litres per 100km into miles per imperial gallon

The basic conversions are:
1 mile = 1.6km
1 imperial gallon = 4.55L

1km = 0.62mi
1L = 0.22 imperial gallon.

All I want really is a formula that can convert xL/100km into ympg

I would like to know how to justify a formula starting with just the above values. I do know what the final formula is, but the L/100km being a fraction kind of throws my understanding of how the formula would work.

Thanks a lot

2. Hello dredgy

Welcome to Math Help Forum!
Originally Posted by dredgy
Hey all. Good to be here. Do need some random conversion help, shouldn't be particularly difficult.

Basically I want to convert litres per 100km into miles per imperial gallon

The basic conversions are:
1 mile = 1.6km
1 imperial gallon = 4.55L

1km = 0.62mi
1L = 0.22 imperial gallon.

All I want really is a formula that can convert xL/100km into ympg

I would like to know how to justify a formula starting with just the above values. I do know what the final formula is, but the L/100km being a fraction kind of throws my understanding of how the formula would work.

Thanks a lot
If we use $x$ L to cover $100$ km, that's $x$ L to cover $100\div 1.6 = 62.5$ miles

So how many gallons are there in $x$ L? Answer $x \times 0.22=0.22x$.

So we've covered $62.5$ miles using $0.22x$ gallons, which is $62.5\div 0.22 x$ miles per gallon.

So there's our formula:

$y=62.5\div 0.22 x$

$= \frac{62.5}{0.22 x}$

$\approx \frac{284}{x}$

So, for example, 8 L per 100 km $\approx \frac{284}{8}=35.5$ mpg