【不耻下问之一】~~~~请教三道数学题!（已解决.感谢!）

cutewen

1.A parking garage rents parking spaces for $10 per week or $30 per month.How much does a person save in a year by renting by the month rather than by the week?
ANSWER: $160

我有点想不通就是10 PER WEEK 那就是一个月40 那一个月便宜10 一年就是$120..怎么都想不到哪有$140

2.The market value of a certain machine decreased by 30 percent of its purchase price each year.If the machine was purchased in 1982 for its market value of $8000, what was its market value two years later?
ANSWER3200

仍然是算不出这个答案.可能是题意理解有问题?

3.A bus trip of 450 miles would have taken 1 hour less if the average speed S for the trip had been greater by 5 miles per hour.What was the average speed S, in miles per hour, for the trip?
ANSWER:45

此题..悲剧的没明白题目在问啥子..


第一次发帖问题目!希望会做的筒子们解答一下哦!解答一题都好!!非常感谢！鞠躬！
问的可能是比较简单的题目。不要见笑啦。俺要继续不耻下问一直问到全部都明白了去考试!

谢谢！

tmsviviane

2. 8000*(1-2*30%)

3. 450/s  - 1=450/(s+5)

草稿纸

领导辛苦了，小的来看看

1。一年365天 / 7 =52个周
2。30% of its purchase price = 30% x 8000 = 2400 ,  就是每年都折旧2400。
3。一辆公车跑一趟450miles，如果速度s快5m/h的话，总时间就少1小时。

不谢！

jtrchina

1：（365/7）*10-12*30=160,although absent of all answers you gave,take it only as a reference.
2："each year" modifies "decreased",not "the purchase price in each of the mentioned year".So it is an issue on simple interest:8000* (1-(2*0.3))
3：450/S-450/(s+5)=1,a simple equation
Hope it helps

cutewen

还没看各位的解答！先谢了！再看！

cutewen

感谢呀。我刚核对下答案 确实是$160

cutewen

错误总结：
第一题答案是$160  错误在于简单的认为一个月4周..一年4*12=48周..
第二题 错误在于折旧的价格是最初的价格。当时我算的是购买价格*0.7*0.7  T.T
第三题 错误在于读题目毛糙了，看半天没懂，总结就是以后需要多做！多看！

现在错比考试错要好的多的多。大家一起加油。

结贴啦！！！以后我会继续发问的