Respuesta :
To solve such questions we will have to observe the fact that this is a repeating decimal number with the repeating figures being 2 and 1 as 21.
Thus, we can represent 1.21212121... as [tex] 1.\overline{21} [/tex]
Let us represent the original number 1.21212121... by the letter "a". Thus,
a=1.21212121...=[tex] 1.\overline{21} [/tex]
Therefore,[tex] a=1.\overline{21} [/tex]..................(equation 1)
Let us now multiply (equation 1) by 100 to get:
[tex] 100a=100\times 1.212121...=121.\overline{21} [/tex].....(equation 2)
Now, when we subtract (equation 2) from (equation 1), we will get:
[tex] 100a-a=121.\overline{21}-1.\overline{21} [/tex]
[tex] 99a=120 [/tex]
[tex] \therefore a=\frac{120}{99} [/tex]
Thus the given number 1.21212121... can be represented as a fraction as [tex] \frac{120}{9} [/tex].
