On a certain day, a bakery produced a batch of rolls at a total production cost of $300. On that day, ~$\frac{4}{5}$~ of the rolls in the batch were sold, each at a price that was 50 percent greater than the average (arithmetic mean) production cost per roll. The remaining rolls in the batch were sold the next day, each at a price that was 20 percent less than the price of the day before. What was the bakery’s profit on this batch of rolls?
$150
$144
$132
$108
$90
生产x个,300/x*4/5*x*1.5+300/x*1/5*x*1.5*(1-20%)-300=132
设:总rolls 为R, 总成本为300, 平均每个roll的成本为300/R
当天卖出总量的4/5,即4R/5,每个售价:(300/R)*(1+50%)=450/R,
当天收入为:4R/5*450/R=360
第二天卖出剩下的,即:R/5,每个售价:(450/R)*(1-20%)=360/R
第二天收入为:R/5*360/R=72
这批rolls的总收入为:360+72=432
profit:432-300=132
坑好多啊!
汗。。。20% less of the day before....132...再次中招
这个题答案不是108吗?