国际顶尖MBA申请交流平台--TOPWAY MBA

标题: 请教两道题 [打印本页]

作者: tanmagic 时间: 2005-10-13 13:12 标题: 请教两道题

If the sequence x₁, x_2,x_{3, …,}x_n, … is such that x₁ = 3 and x_n₊₁ = 2x_n – 1 for n ≥ 1, then x₂₀– x₁₉ =

A. 2¹⁹

B. 2²⁰

C. 2²¹

D. 2²⁰- 1

E. 2²¹- 1

A certain university will select 1 of 7 candidates eligible to fill a position in the mathematics department and 2 of 10 candidates eligible to fill 2 identical positions in the computer science department. If none of the candidates is eligible for a position in both departments, how many different sets of 3 candidates are there to fill the 3 positions?

A. 42

B. 70

C. 140

D. 165

E. 315

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