Discrete Math Homework Question | Mod Explanation | Test Prep

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The discussion revolves around a discrete math homework question involving modular arithmetic, specifically the meaning of "mod" in the context of a problem. The user expresses confusion about the concept and its application, particularly with the equation a = 4 (mod 13). A participant clarifies that this means the remainder when a is divided by 13 is 4, and encourages the user to solve for c = 9a (mod 13). The urgency of the user's upcoming test adds pressure to understand the material quickly.
Bashyboy
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Homework Statement


I attached the problem as file.


Homework Equations





The Attempt at a Solution


I honestly do not know how to solve this problem. I have a test tomorrow, and this is really the only question that I am having difficulty with. I don't really know what mod means, especially in this context. I have tried to read the textbook, but it being rather convoluted, and me being constrained on time, was really quite futile.
 

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Hi Bashyboy! :smile:

a = 4 (mod 13) means that if you divide a by 13, the remainder is 4

(of course, that's the same as saying a - 4 = 0 (mod 13), ie a - 4 is divisible exactly by 13 :wink:)

show us what you get for c = 9a (mod 13) :smile:
 
Bashyboy said:

Homework Statement


I attached the problem as file.

Homework Equations



The Attempt at a Solution


I honestly do not know how to solve this problem. I have a test tomorrow, and this is really the only question that I am having difficulty with. I don't really know what mod means, especially in this context. I have tried to read the textbook, but it being rather convoluted, and me being constrained on time, was really quite futile.
Here's the attachment:
attachment.php?attachmentid=51751&d=1349900977.jpg


"I don't really know what mod means ..." and you have a test on this stuff tomorrow?

WOW !
 
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

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