求助GWD的数学题~~

yigexiaosb · 发表于 2010-10-18 09:41:00

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:

Q30:
Joanna bought only $0.15 stamps and $0.29 stamps. How many $0.15 stamps did she buy?
(1)    She bought $4.40 worth of stamps.
(2)    She bought an equal number of $0.15 stamps and $0.29 stamps.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.
Answer:

澹泓幽客 · 发表于 2010-10-18 10:38:37

1------ 首项 100 末项 300 项数：{300-100}/2+1=101
和（100+300）101/2=20200

2------- 是D吗。。。

求助GWD的数学题~~

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