GWD4 -16

scorpio2rd

Q16:

In the sequence of nonzero numbers t₁, t₂, t₃, …, t_n, …, t_n+1 = t_n / 2 for all positive integers n.  What is the value of t₅?

(1)     t₃ = 1/4

(2)     t₁ - t₅ = 15/16
                    

                                                                                                                              

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: D

不是很明白....怎么做..尤其是(2) 为什么可以成立...多谢

goofytan

1. t3 = t2/2=1/4 --> t4=t3/2, and t5=t4/2=t3/4--> t5=1/16

2. t5 = t4/2 = t3/4 = t2/8 = t1/16 --> t1 - t5 = t1 - t1/16 = 15t1/16 = 15/16 --> t1 = 1 --> t5 = 1/16

so both sufficient alone