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.

Kudos please if you like my explanation!
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Kindly hit kudos if my post helps!

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!

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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