The graph shows the number of computers assembled during each of 6

Question

https://gmatclub.com/forum/download/file.php?id=35801 The graph shows the number of computers assembled during each of 6 consecutive days. From what day to the next day was the percent change in the number of computers assembled the greatest in magnitude ? A. From Day 1 to Day 2 B. From Day 2 to Day 3 C. From Day 3 to Day 4 D. From Day 4 to Day 5 E. From Day 5 to Day 6 zxwlzd.jpg

amanvermagmat · Accepted Answer

day 1 to day 2 = 20 to 12 = 8/20 * 100 = 40% change
day 2 to day 3 = 12 to 18 = 6/12 * 100 = 50% change
day 3 to day 4 = 18 to 10 = 8/18 * 100 = 44.44 % change
day 4 to day 5 = 10 to 16 = 6/10 * 100 =  60% change 
day 5 to day 6 = 16 to 8 = 8/16 * 100 = 50% change

Clearly, day 4 to day 5 is MAX, hence  D answer

chetan2u · Answer

Hi...

1) first point about change in %..
You are correct , it has to be taken for all choices. Increase/ decrease does not matter..
The member has been lucky to get away with this flaw and get Correct answer.

2) Do you have to go for each choice..
NO

Just look at the down ones.. 1-2, 3-4, 5-6..
Each day the drop is 4 boxes...
So 4 boxes on the least boxes previous day will win..
 Nothing but we have same numerator and we are looking for SMALLEST denominator .. visually the lowest is on 5 day so % on that day = 4/8 *100=50%
Now look for the same in increasing days...increase is of 3 boxes..
On 4-5 day it is lowest so 3/5*100=60%
Our Ans

Abhishek009 · Answer

Just visually examine the graph we need to check greater percentage change between -

Day 2 to Day 3  VS  Day 4 to Day 5

Percentage change in Day 2 to Day 3= 50%
Percentage change in Day 4 to Day 5 = 60%

Thus, the correct answer will be (D)

dangeyg · Answer

Used a visual scan technique.
1. In cases where value drop from previous day, % change is going to be -ve so ignoring them. E.g. Day 1 to 2.
2. we have only 2 candidates, Day 2 to 3 and Day 4 to 5., Visual observation says both have same increment over previous day. 
 But Day 4 to 5 has changed value on a smaller denominator then the Day 2 to 3 ...so it wins.
if someone is not from data analytics field then better calculate to verify.

GMATSkilled · Answer

You need to be a little careful here. The question states - percent change in the number of computers assembled has the greatest in magnitude . So your 1st point could get you into trouble but not in this question though!

ScottTargetTestPrep · Answer

Let’s test each answer choice:

A) From Day 1 to Day 2

|(12 - 20)/20| x 100 = |-8/20| x 100 = 40%

B) From Day 2 to Day 3

x 100 = |6/12| x 100 = 50%

C) From Day 3 to Day 4

|(10 - 18)/18| x 100 = |-8/18| x 100 = 44.44%

D) From Day 4 to Day 5

x 100 = |6/10| x 100 = 60%

E) From Day 5 to Day 6

|(8 - 16)/16| x 100 = |-8/16| x 100 = 50%

Answer: D

amitkumarchandan · Answer

Change is percentage can be calculated by understanding the fractional change in the numbers. (if number changes from 6 to 8, then fractional change is |6-8|/6). The denominator will be the first/initial number and the numerator will be the difference between the two numbers. (As magnitude has been asked, negative or positive will not affect the answer).
In this problem, we get following results of subtraction:
1. 8/20
2. 6/12
3. 8/18
4. 6/10
5. 8/16
Options 1 and 3 are eliminated as they are less than option 5 (Same numerator, different denominator) 
Option 2 and Option 5 are same (1/2) hence both eliminated. Option 4 remains, and hence the answer.

Observing the number might not give the solution this easily every time but it helps to sit back and think about the numbers for 2-5 seconds.

EMPOWERgmatRichC · Answer

Hi All,

We're given a graph that shows the number of computers assembled on each of 6 consecutive days. We're asked for the day-to-the-next-day pair that had the GREATEST PERCENT CHANGE in the number of computers assembled. To answer this question, we'll need the Percent Change Formula (and a little math):

Percent Change = (New - Old)/Old = Difference/Original

Day 1-2: 8/20 = 4/10 = 40% 
Day 2-3: 6/12 = 1/2 = 50% 
Day 3-4: 8/18 = 4/9 = 44.4444% 
Day 4-5: 6/10 = 60% 
Day 5-6: 8/16 = 1/2 = 50%

Final Answer:  D

GMAT assassins aren't born, they're made, 
Rich

adkikani · Answer

sachinpoovanna

Can you elaborate your point? We do not care about positive or negative change, just change of magnitude here. Much as a modulus.
What is incorrect about highlighted text?

niks18   chetan2u   Bunuel 
Can I not simply look at the bar graph difference ignoring the denominator (earlier value) here? Is there any
efficient way than to calculate step by step % changes for each option ?

ChiraKaimook · Answer

The question asked for "greatest in magnitude" so we have to find the percentage change that has the highest absolute value.

I used visual reasoning for this one.

1) Look at the absolute change. 
Decreasing: Day 1->2; 3->4; 5->6 has the same absolute change of 8
Increasing: Day 2->3; 4->5 has the same absolute change of 6

2) The highest magnitude will be the one with the lowest denominator 
Decreasing: Day 5 is the lowest among this group so keep Day 5->6 
Increasing: Day 4 is the lowest among this group so keep Day 4->5

3) Calculate only the two candidates
Decreasing: 8/16 = 50%
Increasing: 6/10 = 60%

With this, the question can be done in about 1 min

Argp · Answer

Bunuel   chetan2u   ScottTargetTestPrep

Do you have any suggestion for increasing the calculation speed on such questions?

I crossed the 2 min mark for this question, and I still ended up copying one incorrect value, which led to incorrect calculation.

Any tip is much appreciated! Have a great day!

EMPOWERgmatRichC · Answer

Hi Argp,

To start, assuming that you use all of your time when working through the Quant section of the Official GMAT AND answer all of the questions in that section, then your AVERAGE time will be 2 minutes per question. That does NOT mean that you should plan to spend 2 minutes on each question though - and that type of a goal is NOT good pacing advice.

In addition, most GMAT questions can be approached in more than one way, so if you find that you're taking too long to answer certain questions, then you have to consider how you're going about working through the prompt (how many times do you read the prompt, are you trying to do work "in your head" and making little mistakes, how effectively do you take notes and in the case of anything calculation-related - how are you performing your calculations). 
 
GMAT assassins aren't born, they're made,
Rich

ScottTargetTestPrep · Answer

Solution:

In general, no. If the numbers were such that the actual value of the difference was the same between each day and next day pair, then we would be able to conclude that the day with the smallest number of assembled computers would have the greatest change as a percentage (for instance, an increase from 5 to 10 represents a greater percent increase compared to an increase from 20 to 25, even though the actual value of the increase is 5 for both scenarios); however, we don’t have that situation in this question. We basically need to compute each percent change and compare. The only way to improve time on such questions is to improve the speed of calculation of a percent change.

Himabinduj · Answer

We don't need to calculate percentages here.
we can quickly calculate below fractions for day1-2, day2-3,day3-4, etc..

1) \frac{8}{20}

2) \frac{6}{12}

3) \frac{8}{18}

4) \frac{6}{10}

5) \frac{8}{16}

Now compare 1,3 & 5(same numerators) --> we know that "the lesser the denominator, the higher is the value of the fraction" so   \frac{8}{16}   wins
Now compare 2 and 4(same numerators) --->with the same logic as above   \frac{6}{10}  wins
Now between  \frac{8}{16}  (which is  \frac{1}{2}  =0.5) and \frac{6}{10}  (which is 0.6) --  \frac{6}{10}    wins (i.e.,day 4-5)

So option D is the answer.

GMATinsight · Answer

Answer: Option D

Video solution by  GMATinsight

https://www.youtube.com/watch?v=TpF2U73b4LQ

avigutman · Answer

Video solution from Quant Reasoning: Subscribe for more: https://www.youtube.com/QuantReasoning? ... irmation=1 https://www.youtube.com/watch?v=aSMjzwLpgWg

Fish181 · Answer

can someone explain why we can't just look at the magnitude of the numbers without calculating percent change to get the correct answer? Seems like the two days that have the largest difference in numbers would just be the correct answer but it isn't.

Bunuel · Answer

We can't just look at the numbers. We need the percent change, not just the difference in numbers of computers produced. While it might seem like the days with the biggest difference in computer assembly should be the ones with the greatest change, that's not how it works. Take Day 1 to Day 2, for example. There's an 8 computer difference, but it's only a 40% change. Compare that to Day 4 to Day 5, where there's just a 6 computer difference, but it's a whopping 60% change.

EtaCarnia · Answer

I am not really sure how the difficulty level is assigned to the questions in GMAT club. Can somebody help me?

The graph shows the number of computers assembled during each of 6

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