Official Guide Explanation:
Problem Solving #98




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Solution and Metadata

Question: 98
Page: 166
Difficulty: 5 (Moderate)
Category 1: Word Problems > Rate Problems > other
Category 2: Arithmetic > Powers and Roots of Numbers > Powers

Explanation: When working with a sequence (a series of numbers that change in a given pattern), it's useful to assign a value or a variable to one term in the sequence and apply the pattern. The idea is this: say that the "intensity corresponding to a reading of 3" is x. If a reading of n + 1 has 10 times the intensity o fa reading of n, that means a reading of 4 (one greater than 3) has ten times the intensity of a reading of 3, or 10x . Similarly, a reading of 5 has an intensity of 10(10x). See a pattern emerging? Every time 1 is added to the reading, the intensity is multiplied by ten. So, the difference between readings of 8 and 3--1 is added five times--is 10(10)(10)(10)(10), or 105, choice (C).

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