问题详情

In 1980, the cost ofp pounds of potatoes was d dollars. In 1990, the cost of 2p pounds of potatoes was d/2 dollars. By what percent did the price of potatoes decrease from 1980 to 1990？
A．25%
B．50%
C．75%
D．100%
E．400%请帮忙给出正确答案和分析，谢谢！