कोई बात नहीं  =  indeclinable
`Thanks very much for your help.' `not at all, it was a pleasure.'

कोई बात नहीं  =  it's all right
`Thanks very much for your help,' `not at all, it was a pleasure.'

बिल्कुल नहीं  =  no
`Did you mind if i open the window' `not at all.'