One DS

redpot

Is 5^* less than 1000?

1). 5^(*-1)>3000
2). 5^(*-1)=5^*-500

The answer is said to be B.  Why not D?

ianwang

5^* less than 1000: X<=4 1). 5^(*-1)>3000: X>=6 NOT 2). 5^(*-1)=5^*-500: X=4 YES S0, B.

tongxun

答案应该为D。5^n=1000, 5^3 *8=1000 1）5^(n-1)>3000 ---5^n >15000, so 5^n >1000 2)5^(n-1)=5^n -500 ---5^n=625, so 5^n <1000

redpot

Yes, I think the answer should be D because either of them can tell WHETHER  5^* is  less than 1000 OR NOT.  However, the answer was said to be B.  It might be a wrong key, right?