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The table above shows the closing price of a stock during a week. If

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The table above shows the closing price of a stock during a week. If [#permalink]

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New post 13 Oct 2017, 00:18
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The table above shows the closing price of a stock during a week. If the average (arithmetic mean) closing price for the five days was $75.50, what was the closing price on Friday?

A. $75.35
B. $75.40
C. $75.42
D. $75.45
E. $75.48

[Reveal] Spoiler:
Attachment:
2017-10-13_1116.png
2017-10-13_1116.png [ 9.74 KiB | Viewed 587 times ]
[Reveal] Spoiler: OA

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Re: The table above shows the closing price of a stock during a week. If [#permalink]

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New post 13 Oct 2017, 01:00
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Let the Closing price on Friday= x

\(\frac{75.58+75.63+75.42+75.52+x}{5}\)= 75.50

\(\frac{302.15+x}{5}\)= 75.50

302.15+x= 377.50
x= 377.50-302.15= 75.35
x= 75.35

Answer: A.

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Re: The table above shows the closing price of a stock during a week. If [#permalink]

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New post 13 Oct 2017, 01:42
Here,
Let the Closing price on Friday= x

75.58+75.63+75.42+75.52+x575.58+75.63+75.42+75.52+x5= 75.50

302.15+x5302.15+x5= 75.50

302.15+x= 377.50
x= 377.50-302.15= 75.35
x= 75.35

Answer: A.

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The table above shows the closing price of a stock during a week. If [#permalink]

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New post 14 Oct 2017, 16:54
Another approach I've come to admire for these kind of questions.

Think how far off each of these amounts are from the Mean.

Monday: 75.58 --> Exceeds mean by 0.08
Tuesday: 75.63 --> Exceeds mean by 0.13
Wednesday: 75.42 --> Fall shorts from mean by 0.08
Thursday: 75.52 --> Exceeds mean by 0.02

Excess: 0.08 + 0.13 + 0.02 = 0.23
Short: 0.08

Excess > Short; So right now the sum of these 4 amounts exceed the Mean by 0.15 (0.23 - 0.08)

Our 5th amount should be something that compensates for the excess i.e. it should be 0.15 less than Mean which brings us to
75.35

This method has minimal calculations meaning fewer chances you mess up during calculations.

Don't forget the kudos if this helped ya!

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Re: The table above shows the closing price of a stock during a week. If [#permalink]

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New post 14 Oct 2017, 19:12
1. Calculate the variance between each number and the mean.

- Variance between 75.58 and the mean (75.5) is +0.08
- Variance between 75.63 and the mean (75.5) is +0.13
- Variance between 75.42 and the mean (75.5) is -0.08
- Variance between 75.52 and the mean (75.5) is +0.02

2. Let the variance between the closing price on Friday and the mean be x

3. 0.08+0.13-0.08+0.02+x=0
Then x=-0.15

4. So the Closing Price on Friday is:
Mean + Variance = 75.5+(-0.15) = 75.35

Answer is A

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Re: The table above shows the closing price of a stock during a week. If [#permalink]

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New post 16 Oct 2017, 17:20
Bunuel wrote:
Image
The table above shows the closing price of a stock during a week. If the average (arithmetic mean) closing price for the five days was $75.50, what was the closing price on Friday?

A. $75.35
B. $75.40
C. $75.42
D. $75.45
E. $75.48

[Reveal] Spoiler:
Attachment:
2017-10-13_1116.png


We can let x = the closing price on Friday, and thus:

(75.58 + 75.63 + 75.42 + 75.52 + x)/5 = 75.50

(302.15 + x)/5 = 75.50

302.15 + x = 377.50

x = 75.35

Alternate Solution:

Since we are given that the average for the five days was 75.50, let’s compare each of the four given days to the average.

Mon Tues Wed Thurs
+0.08 +0.13 -0.08 +0.02
Notice that +0.08 will cancel with -0.08; therefore, the total net gain from the 4 days is +0.15. Thus, we must have -0.15 on Friday to counter the net gain of +0.15, and so the closing price on Friday must be 75.50 - 0.15 = 75.35. (Note: When a list of numbers is given (but one of them is missing) and the average of the numbers is given, this method of finding the missing number is most useful when the given numbers are pretty close to the average.)

Answer: A
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Re: The table above shows the closing price of a stock during a week. If   [#permalink] 16 Oct 2017, 17:20
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