[求助]prep数学几道题

wangzilin

请好心人帮我解答一下，prep几道数学题

A used-car dealer sold one car at a profit of 25percent of the dealer's purchase price for that car and sold another car at a loss of 20 percent of the dealer's purchase price for that car. if the dealer sold each car for 20,000 what was the dealer's total profit or loss, in dollars, for the two transactions combined?

我算 20000×25%-20000×20%= 1000profit
结果是1000loss. 为什么呢？

三个数的平方相加等于75.，三个数的和可能是多少？

一个圆直径OR的值为18，一个玄PQ与它平行 并且两条平行线的内错角是35度。 请问这个弦的大小？ 正确答案是2pai.
请帮我解答这几个问题

ziqiangel

1，设买入价为x

x*1.25=20000   x=16000

第二辆买入y

y*0.8=20000   y=25000

故买入花了x+y=41000