Questions about the world of GRE Math from other sources and general math related questions.
shannon5000
Course Students
 
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GRE OG pp,219-220 q.3,15

by shannon5000 Wed Apr 23, 2014 5:31 pm

For question#3 it asks which of the following numbers are divisible by 8. Even though I figured it out, what is the divisibility rule for 8 so I can figure this out faster?

For question#15 it states: When the positive integer n is divided by 3, the remainder is 2 and when n is divided by 5, the remainder is 1. What is the least possible value of n?

I would greatly appreciate an explanation to the answer.

Thanks in advance!
tommywallach
Manhattan Prep Staff
 
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Re: GRE OG pp,219-220 q.3,15

by tommywallach Tue Apr 29, 2014 12:25 pm

Hey Shannon,

Not sure what you mean by the divisibility rule for 8. There is a general divisibility rule for all numbers, known as the factor foundation rule, which states that "if x has all the prime factors of y, x is divisible by y." Applied to 8, that would mean that any number that has all the prime factors of 8 (2, 2, and 2) is divisible by 8.

For your second question, the only way to solve is to look at possible values of n.

Numbers that give you a remainder of 2 when divided by 3: 2, 5, 8, 11, 14, etc.

Numbers that give you a remainder of 1 when divided by 5: 1, 6, 11, 16, 21, etc.

The first value of n that fits both criteria is 11.

Hope that helps (and sorry for the delay)!

-t