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High School Math - What am i doing wrong here?

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High School Math - What am i doing wrong here? [#permalink] New post 14 Aug 2010, 03:43
Can someone please explain me what is the wrong with the Example2 below. Eventhough the same approach, Example 1 is giving me the correct answer but Example2 is giving me the wrong answer.

**Note: If you find the below data is not properly formated, please see the attachment for the same ***
Example1: Divide 113 by 4

Step1:
4)113(
Step2:
4)113(2
8
-------
3 /* 11 – 8 = 3 */
Step3:
4)113(2
8
-----
33 /* Import 3 from Top */
Step4:
4)113(28
8
-----
33
32
-------
1
Step5:
4)113(28.
8
-----
33
32
-------
10 /* Place a point after 28 and put a Zero after 1 - Do you agree with this? Atleast i agree!*/

Step6:
4)113(28.25
8
-----
33
32
-------
10
8
--------
20
20
--------
0
To make sure what we got is correct: 28.25 * 4 = 113

Now, Example2: Divide 123 by 4
Step1:
4)123(
Step2:
4)123(3
12
----
0 /* 12 –128 = 0 */
Step3:
4)123(3
12
-----
03 /* Import 3 from Top */
Step4:
4)123(3.
12
-----
30 /* Put a point after 3 in Left brackt and place a zero after 3 (As i agreed in Example 1) */

Step5:
4)123(3.7
12
-----
30
28
-------
2

Step6:
4)123(3.75
12
-----
30
28
-------
20
20
--------
0
Answer Validation: 4 * 3.75 IS NOT EQUAL TO 123

What is the wrong I am doing here?


Cheers!
Ravi
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Last edited by nravi4 on 14 Aug 2010, 04:03, edited 1 time in total.
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Ms. Big Fat Panda
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Re: High School Math - What am i doing wrong here? [#permalink] New post 14 Aug 2010, 03:56
Expert's post
Well for starters, once you're done dividing the 12 part of 123 by 4, and you bring the 3 down, you have to put a zero on the quotient side before you can add a zero to the 3 to make it 30.

So it should be

4)123(30.75
12
--------------
03
0
------------
030
028
------------
0020
0020
------------
0

So the answer is 30.75. I mean this is basic math and you don't need to do long division at all. 4*3 = 12, so 4*30 = 120 < 123, so you know that your answer has to be greater than 30.
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Re: High School Math - What am i doing wrong here? [#permalink] New post 14 Aug 2010, 04:07
Mr whiplash2411,

Thank you for response. But why do i have to put 0 first in quotient side? I didn't do the same thing in Example1 before putting a point in quotient side.

Cheers!
Ravi
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Ms. Big Fat Panda
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Re: High School Math - What am i doing wrong here? [#permalink] New post 14 Aug 2010, 15:20
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Expert's post
The basic rule is, everytime you bring one digit down for division, you check for divisibility. So in this case, 12 is divisible and you get 3 on the side. When you bring the 3 down, 3 is NOT divisible by 4, so you put a zero on the quotient, before adding a 0 to the 3, making it 30 and then proceeding with the decimal point. In the first example, when you divide 11 by 4, you get 2, and you get a REMINDER from this which is 3, and then you bring the 3 down and hence check for divisibility of 33. And 33 > 4 so you add the 8 there.

Whenever you bring a digit down from the main number you're dividing you must check for divisibility. If the number you've brought down is less than the divisor itself, you add a zero. But in terms of checking for results, think about in terms of common sense. Does 3.75*4 being equal to something near 120 make sense? No. That's a way to cross check.

And just for reference, it's a miss. Not Mr.

Hope this helps. If not, refer the math book at GMAT Club for further references on the number properties and divisibility and so on.

Quote:
But why do i have to put 0 first in quotient side? I didn't do the same thing in Example1 before putting a point in quotient side.


You didn't add the zero because when you brought the 3 down, there was already a reminder there. So you made the number 33 and then added an 8 there. Here the initial reminder is a 0 and when you bring the 3 down, it stays as 03 and hence you add a 0 to the quotient because obviously 3 is not divisible by 4, being smaller than it.
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Re: High School Math - What am i doing wrong here? [#permalink] New post 15 Aug 2010, 10:55
Miss whiplash2411,

I am more worreid about the mistake i am doing in Example2, rather than results or answer validations, and your above explanation spot on clarified my doubt.

Appreciate your inputs.

Cheers!
Ravi
Re: High School Math - What am i doing wrong here?   [#permalink] 15 Aug 2010, 10:55
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