Let,

x = 0.125125125 ….equation 1

As 125 is the repeating term, so in all such problems multiply both sides of the equation with a number such that complete repetitive part of number comes after the decimal.

∴ multiplying equation 1 with 1000 in both sides, we have –

1000x = 125.125125125… …equation 2

Subtracting equation 1 from equation 2,we get-

1000x – x = 125.125125125… - 0.125125125….

⇒ 999x = 125

∴ x = 125/999