How do I work out how a number is written in fraction form, if it is a reoccurring decimal?

If I have a reocurring decimal I use a special trick to work it out as a fraction. The trick is to try and cancel out the reocurring bit by multiplying by 10 several times and then using subtraction.
E.g. 7.999999... where 9 is reocurring.First define x as the decimal we are interested in. x=7.999..Next we would multiply x by 10 to get 10x=79.99999...We do this because we know that subtracting x from 10x would cancel out the reocurring bit to give 9x=79-7=72.If 9x=72, then dividing everything by 9 gives x=72/9.