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. 10100 B.20200 C.22650 D40200 E.45150
all the even integers between 99 and 301: (301-99)/2=101
the sum of these: [101(101+1)]/2
A jar contains 16 marbles, of which 4 are red, 3 are blue, and the rest are yellow. If 2 marbles are to be selected at random from the jar, one at a time without being replaced, what is the probability that the first marble selected will be red and the second marble selected will be blue?
A. 3/64 B.1/20 C.1/16 D.1/12 E.1/8
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Thank you for your help
提问时间：2010-01-11 18:50:39提问者： Kathy00097 [初中生]
28:Here first term is a=100
回答时间：2010-01-12 11:55:32 回答者：zsk_koo [知识堂达人]