material quantity wrong posting

Hi Experts,

here i got a situation, i.e in the receipt of goods, the quantity of a 10 bags worth of 10000, it was posted correctly. but the each bag contains 12 pieces, total 120 pieces where as it calculated wrongly by our clerk as 100 pieces.

hence the inventory calculated 10 bags and 100 pieces as Rs.10000, instead of 10 bags with 120 pieces Rs.10000.

without effecting the prices, how to change this. this transaction entered throu 561and affected in production also.

its little bit urgent.....kindly suggest me

raghav