Sleeping Powder

A doctor told a Kerryman to give his wife as much sleeping powder as would cover a lOp piece. When the doctor called a week later to see his patient the Kerryman said
'She's been sleeping for over six days'!
'Did you give her the sleeping powder exactly as I prescribed?' asked the doctor.
'Not exactly', said the Kerryman, 'I didn't have a tenpenny piece so I used five twopenny pieces instead'.