Consider the following procedure for dividing the three-digit number 3 7 5 by 8 :
Write down the number formed by the first two digits, namely 3 7 .
Multiply this by 2 to get 7 4 .
Add to this, the units digit of 3 7 5 (the original number), obtaining 7 4 + 5 = 7 9 .
Then divide it by 8 to get 9 with a remainder of 7 .
Add this result ( 9 , remainder 7 ) with 3 7 (the first two digits of the original number) to get your answer: 4 6 , remainder 7 .
Thus 3 7 5 divided by 8 equals 4 6 with a remainder of 7 .
Does this method always work for three-digit numbers? Why, or why not?
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While I understand what you are attempting to say, it is not expressed clearly. I am concerned that someone who doesn't already know how to solve this problem, would not be unable to understand what you are saying.
Lovely Problem! @Satyajit Mohanty
Lovely Solution! @Mehul Arora
While I understand what you are attempting to say, it is not expressed clearly. I am concerned that someone who doesn't already know how to solve this problem, would not be unable to understand what you are saying.
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@Calvin Lin Which part of my solution should I improve?
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Overall, make it much clearer why/how "the remainder when xyz is divided by 8 equals the remainder when (20x+2y+z) is divided by 8. While I see the steps involved, that explanation of the steps is not presented.
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@Calvin Lin – @Calvin Lin I cleaned up my solution a bit. Is it better now? If anything needs to be changed, I'll do that Tomorrow morning :)
Additional info:- I have a younger brother but he's only 9 years. So pretty much, he won't be able to understand all of this stuff :P
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@Mehul Arora – Haha, well not a younger brother than, but a friend who hasn't solved this problem.
It still doesn't address the concerns that I brought up above. You have not explained why "the remainder when xyz is divided by 8 equals the remainder when (20x+2y+z) is divided by 8", which is the point of the solution.
You have all of the steps needed, but you do not have the phrasing / logical connections between these statements.
Let the number be a b c . The successive steps have us calculate: a b ; 2 a b ; 2 a b + c ; 8 2 a b + c ; a b + 8 2 a b + c = 8 1 0 a b + c = 8 a b c .
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Basic Knowledge: Any Three digit number will be in the form of 1 0 0 x + 1 0 y + z where x is it's hundred's digit, y is the tens digit and z is the units digit. E.g. 341= 1 0 0 × 3 + 1 0 × 4 + 1
x y z represents the number as a value. If we write that the number = x y z it might be percieved for x × y × z
Let the number be here x y z = 1 0 0 x + 1 0 y + z
According to the procedure, The number formed by the first two digits = x y = 1 0 x + y
Multiply by two to get 2 0 x + 2 y
Adding the units digit, we get 2 0 x + 2 y + z
Divide it by Eight. 8 2 0 x + 2 y + z
Let us ignore the step where we get the remainder and the quotient and we add them to the original two digit number, because it makes no difference whether we divide and add or we add first and divide. (E.g. We break a number 341 into 100+241. We divide them individually by 8 getting remainders 4 and 1. We add them, and we get 5 as the remainder which is the remainder when 341 is divided by 8).
Instead, we directly add our number i.e. 8 2 0 x + 2 y + z to our original two digit number.
Adding, 8 8 0 x + 8 y + 2 0 x + 2 y + z
⇒ 8 1 0 0 x + 1 0 y + z
⇒ 8 x y z Thus this would give us the remainder and the quotient when the original there digit number is divided by 8
Woot! Thus we get the desired result and the method works!. :)