OG 12 5.5.195题目未读懂，求帮助

hlaboratory

A store currently charges the same price for each towel that it sells. If the current price of each towel were to be increased by $1, 10 fewer of the towels could be bought for $120, excluding sales tax. What is the current price of each towel?

treewing929

X=charge per towel
T=no. of towel originally

XT=120
(X+1)(T-10)=120
XT-10x+T-10=120
120-10X+120/X=130
-10x+120/X=10
X^2+X-12=0
(X+4)(X-3)=0
X=3 or X=-4(rejected)

hlaboratory

求大侠能用中文说明题目是什么意思吗？

vilanyu

另一种等式的解法：
设P为现在的价格，P-1为原始价格
那么就有
(120/P-1) - (120/P) = 10
等式最后可以化成
P^2 - P -12 =0
配平（P+3）(P-4)=0
P=4
现有价格为4刀，原始价格为3刀

airphone

商店里每条毛巾标价相等。如果每条毛巾价格上涨1$,那么对于120$来说，能比原价少买10条毛巾，不含税，问涨价前的价格。