remainder question

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remainder question

by henilshaht » Fri Dec 06, 2019 6:36 am
P and Q are integers, and r is the remainder when P is divided by Q. If P = 3.16Q, which of the following must divide evenly into r?
I. 2
II. 4
III. 8

A. I Only

B. II Only

C. I and II

D. II and III

E. I, II, and III
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by [email protected] » Fri Dec 06, 2019 11:00 am
Hi henilshaht,

To start, when posting questions, you should make sure to include the correct answer.

With this prompt, we're told that P and Q are INTEGERS, R is the REMAINDER when P is divided by Q and P = 3.16Q. We're asked which of the following MUST divide evenly into R (which really means "which of the following will ALWAYS divide evenly into R regardless of what R actually is?"). This question is based on a couple of math patterns - and we can TEST VALUES to prove what those patterns are.

To start, the three numbers to consider are 2, 4 and 8 (which are all EVEN numbers). The five answer choices each include at least one of the Roman Numerals, so we know that R must be an EVEN number and we can eliminate a couple of answers immediately based on the rules of Arithmetic. Any number that is divisible by 8 will ALSO be divisible by 4 and 2.... and any number that is divisible by 4 will ALSO be divisible by 2. Thus, Answer B and D cannot be correct (since they include "just 4" and "just 4 and 8" without including "2").

Since both P and Q are INTEGERS, we have to multiply the (3.16) by an integer that will eliminate the decimal points. The most obvious number would be Q = 100, which would make P = 316. In this situation, we have....
P/Q = 316/100 = 3 remainder 16.... meaning that R = 16

This is NOT the only possible value for R though. Since both 316 and 100 are EVEN numbers, that fraction can be reduced. When we divide both numbers by 2, we get...

P = 158 and Q = 50
P/Q = 158/50 = 3 remainder 8.... meaning that R = 8

This is still NOT the only smallest possible value of R though. Since both 158 and 50 are EVEN numbers, that fraction can be reduced. When we divide both numbers by 2, we get...

P = 79 and Q = 25
P/Q = 79/25 = 3 remainder 4.... meaning that R = 4.

At this point, we cannot reduce the fraction any further, so we now have the smallest possible value of R. In this situation, "8" will NOT divide evenly into R, but "4" and "2" will. Those two values are the only ones that MUST divide into R ("8" sometimes does, but sometimes does not).

Final Answer: C

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by GMATGuruNY » Fri Dec 06, 2019 11:13 am
henilshaht wrote:P and Q are integers, and r is the remainder when P is divided by Q. If P = 3.16Q, which of the following must divide evenly into r?
I. 2
II. 4
III. 8

A. I Only

B. II Only

C. I and II

D. II and III

E. I, II, and III
When one positive integer is divided by another, we typically represent what's left over either as a REMAINDER or as a DECIMAL.
There is a relationship between the two representations:

Remainder/Divisor = Decimal.

When 5 is divided by 2:
Remainder representation: 5/2 = 2 R1
Decimal representations: 5/2 = 2.5
Remainder/Divisor = 1/2
Decimal = 0.5
Since the two values are equal:
Remainder/divisor = decimal.

We should write the decimal representation AS A FRACTION IN ITS MOST REDUCED FORM.

In the problem above:
Remainder = R
Divisor = Q
Decimal = 0.16 = 16/100 = 8/50 = 4/25
R/Q = 4/25

Since R/Q is in its most reduced form, we know that Q must be a multiple of 25 and that R must be a multiple of 4.

Options I and II (2 and 4) will divide evenly into every multiple of 4.
Option III (8) will not divide evenly into R if R = 4, 12, 20, etc.

The correct answer is C.

For a similar problem in the OG13, check here:

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