OG上几道数学题，各位NN,SOS

babff

请各位NN把这8道题目分析一下，并用中文解释一下到底该怎么作？？？小弟不甚感激。。。。。。。。。。

OG12.157.   For any positive interger n,the sum of the first n positive intergers equals n(n+1)/2.What is the sum of all the even intergers between 99 and 301?

A.10100 B.20200 C.22650 D.40200 E.45150

OG12.78   Leona bought a 1-year,$10000 certificate of deposit that paid interest at an annual rate of 8 percent compounded semiannually. What was the total amount of interest paid on this certificate at maturity?

A.$10464 B.$864 C.$816 D.$800 E.$480

OG12.151  A toy store regularly sells all stock at a discount of 20 percent to 40 percent. If an additional 25 percent were deducted from the discount price during a special sale,what would be the lowest possible price of a toy costing $16 before any discount?

A.$5.6     B.$7.2   C.$8.8     D.$9.6     E.$15.2

OG11绿皮91.For a light that has an intensity of 60 candles at its source, the intersity in candles, S, of the light at a point d feet from the source is given by the formula S=60k/（d的平方），where k is a constant. If the intersity of the light is 30 candles at a distance of 2 feet from the source, what is the intersity of the light at a distance of 20 feet from the source?

A 3/10 candles   B.1/2    C.1   D.2       E.3   (单位一样）

OG11绿皮151.A box contains 100 balls,numbered from 1 to 100.If three balls are selected at random and with replacement from the box ,what is the probability that the sum of the three numbers on the balls selected from the box will be odd?

A.1/4   B 3/8    C 1/2   D 5/8     E 3/4

OG11绿皮44.What is the maximum number of 5/4 foot pieces of wire that can be cut from a wire that is 24 feet long?

A.11   B.18   C.19   D.20   E.30

OG11绿皮49.A certain fishing boat is chartered by 6 people who are to contribute equally to the total charter cost of $480.  If each person contributes equally to a $150 down payment,how much of the charter cost will each person still owe?

A  $80    B.$66  C.$55  D.%50    E.$45  

OG11绿皮120.One week a certain truck rental lot had a total of 20 trucks, all of which were on the lot Monday morning .If 50 percent of the trucks that were rented out during the week were returned to the lot on or before Saturday morning of that week, and if there were at least 12 trucks on the lot that Saturday morning, what is the greatest number of different trucks that could have been rented out during the week?

A.18   B.16   C.12   D.8   E.4

coolboxer

OG11绿皮120.One week a certain truck rental lot had a total of 20 trucks, all of which were on the lot Monday morning .If 50 percent of the trucks that were rented out during the week were returned to the lot on or before Saturday morning of that week, and if there were at least 12 trucks on the lot that Saturday morning, what is the greatest number of different trucks that could have been rented out during the week?

A.18   B.16   C.12   D.8   E.4

选B

at least 12 trucks on the lot that Saturday morning 可以推出至多有8辆车在外面。

再根据50%那个条件，就是8*2，得16