Item cost for Purchase item

Hi,

We have land into following scenario:

We were using Item-ABC in formula as WIP item and cost was generating for this item using STD costing, now we have purchased this item after 3 month (we never purchased previously).

Now, ACT cost in previous period (i.e. FEB14) have was ZERO because this is not purchase item but in MAR-14 we have purchased this item with 100 Rupees cost

What happening in ACT Cost calculation is:

Previous Period Qty=1000 and prev. period cost=0

Current period purchased qty=1000 with cost of 100

hence as per below calculation average cost is getting 50 Rupees where as we have purchase item with 100 Rs.