Help!!! PS 這題怎麼解?!

babywong

各位. please help. Why is answer C?

On a scale that measures the intensity of a certain phenomenon, a reading of n +1 corresponds to an intensity that is 10 times the intensity corresponding to a reading of n. On that scale, the intensity corresponding to a reading of 8 is how many times as great as the intensity corresponding to a reading of 3?

(A) 5
(B) 50
(C) 10^5
(D) 5^10
(E) 8^10-3^10

Answer: C

fly12404

n+1 比n 強度大十倍 => n+2比n大十的平方倍.........類推
8-3 =5
=> 10的五次方 : )

Luxe

这个题 可以化简称 这个意思，有一个数列，有如下的关系，第n+1项是 第n项的10倍，现在问，第8项是第3项的多少倍，就是10^5

yzg1236

度数大1，代表强度大10倍，设强度为Dn, n为读数
那么D4=10 *D3，D5=10 * D4 = 10 * （10 * D3）。。。 D8 = 10^5 * D3

babywong

Thank you!!!! I have more questions.

A store reported total sales of $385 million for February of this year. If the total sales for the same month last year was $320 million, approximately what was the precent increase in sales?
(A) 2%
(B) 17%
(C) 20%
(D) 65%
(E) 83%

afei0128

Thank you!!!! I have more questions.

A store reported total sales of $385 million for February of this year. If the total sales for the same month last year was $320 million, approximately what was the precent increase in sales?
(A) 2%
(B) 17%
(C) 20%
(D) 65%
(E) 83%

-- by 会员 babywong (2010/7/30 9:11:31)

(385-320)/320=20.4%
选C

babywong

為什麼是除以 320 last year? 不是 385 this year? 因為我是除以 385.

afei0128

这是一个关于增长率的概念问题吧~
A比B大了多少的公式为：(A-B)/B

babywong

了解! 謝謝你們!!!!

another question....

If X is the product of the positive integers from 1 to 8, inclusive, and if i, k, m and p are positive integers such that X=2^i 3^k 5^m 7^p, the i+k+m+p=
(A) 4
(B) 7
(C) 8
(D) 11
(E) 12

yzg1236

X = 8！= 2 * 3 * 4 * 5 * 6 * 7 * 8
           = 2 * 3 * (2的2次方) * 5 * (2 * 3) * 7 * (2的3次方)
           = (2的7次方) * (3的2次方) * 5 * 7

题目说  X=2^i 3^k 5^m 7^p
因此 i=7, k=2, m=p=1

D