During a one-day sale, a store sold each sweater of a certain type for $30 more than the store's cost to purchase each sweater. How many of these sweaters were sold during the sale?
(1) During the sale, the total revenue from the sale of these sweaters was $270.
(2) During the sale, the store sold each of these sweaters at a price that was 50 percent greater than the store's cost to purchase each sweater.
Ans:C
條件- S=C+30
設賣出x件
(1) Sx-Cx=270 條件代入
(C+30)X-CX=270 30X=270 X=9件---SUFFICIENT
(2)2s=3C therefore we get S and C
but we do not know X---------------------insufficient
therefore I chose A
