the decimal expansion of the rational number 31/ 2² _*5 will terminate after

it will terminate after 2 places because the denominator is in the form 2^m * 5ⁿ whose so ever power is greater like here in this question power of 2 is greater then the power of 5 therefore it will be 2
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Now if a number is of type , where n is not a multiple of 2 or 5, then the number of digits after zero in this number will be either a and b, whichever is greater.