GWD31-1-26/28

shiftmonkey

Q26:

Running at their respective constant rates, machine X takes 2 days longer to produce w widgets than machine Y.  At these rates, if the two machines together produce 5/4 w widgets in 3 days, how many days would it take machine X alone to produce 2w widgets?

 A.      4

 B.      6

 C.      8

 D.     10

 E.      12

 Answer: E

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Q28:

For any positive integer n, the sum of the first n positive integers equals [n(n+1)]/2.  What is the sum of all the even integers between 99 and 301?

 

A.      10,100

B.      20,200

C.      22,650

D.     40,200

E.      45,150

Answer: B

麻烦NN解答一下怎么算出来的，一直想不出，谢谢。

jockey829

w/x+w/x-2=5/4w/3

所以x=6  6*2w=12

第二个貌似等差数列，(100+300)*101/2=20200

jockey829

LZ几号考啊....

shiftmonkey

谢谢楼上指点。

Q28其实根本不需要前面的条件，直接用等差数列求和就可以，我就是被它这个条件弄糊涂了。

汗……，我还没报名呢，一战之后一直没敢报