Hello,
provided that the ...456... is repeated endlessly then the decimal can be transformed into a fraction.
Let x = 0.21456456456456...
1. The non-repeating part contains 2 digits. Now multiply x by 10². You get:
100x = 21.456456456456...
2. The repeating part contains 3 digits. Now multipy the result of 1. by 10³. You get:
100000x = 21456.456456456456...
3. Subtract both results:
99900x = 21435. Solve for x: