Decimal – fraction calculation

It's 4.30 rather

The quickest way depends on your knowledge of fractional times tables.  The sure way is to multiply through until there are only zeroes after the decimal point and then divide top and bottom through by each of the prime numbers as many times as they will go without producing decimals.

The 4.33 example is tricky because the decimal would need to be infinitely recurring to give 10/3.  Otherwise it's 433/100 because 433 is a prime number.  You'd need to attempt prime factors up to about 20 in your head if you didn't know that.  If you recognise the figures after the decimals (say .33... is a third) then you have the answer.

In summary, the best way is to learn them backwards.  Lots of bookies can convert a lot faster than I can even though my intelligence and mathematical ability is massively greater.

mine are obviously fkd

I'd imagine in the 4.X example it'd be best to ignore the 4 as it just complicates things and just look at the .33 and just know what is best to fit into that, i.e. (4).4 would be .. 2/5, then add the 4 (3) bit on so that would be 3 * 5 + 2 = 17/5?
Then if obviously can be reduced, reduce it. I never work in fractional odds, don't like them.
There are only so many fractions that are used so above idea might reduce the work.

i'm surprised anyone still works in fractional odds ,especially on here

Its like moving to France and not learning French