A shopkeeper estimates annual requirement of an itemas $2000$ units. He buys from supplier $10$ per item andthe cost of ordering is $50$ birr each time. If the stockholding costs are $25\%$ per year of stock value howfrequently should replenish his stock? Further, supposethe supplier offer $10\%$ discount on order between $400$and $699$ item, a $20\%$ discount on order exceeding orequal to $700$ can the shopkeeper reduce his cost bytaking advantages from either of the discount $?$