The shortage of 10 kg is a reasonable loss in transit, so the actual cost per kg is 17600/490=35.92 yuan.

In fact, the actual total cost of purchased materials has not changed, but the unit cost has changed, while the planned cost =35*490= 17 150 yuan.

Cost variance amount of this batch of warehousing materials = actual cost-planned cost =17600-17150 = 450 yuan.