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Marks in statistics of 12 students are x, 28, 35, 56, 78, 63, 65, 81, 79, 83, 80, y, where x and y are the lowest and highest marks, respectively
Question

Marks in statistics of 12 students are x, 28, 35, 56, 78, 63, 65, 81, 79, 83, 80, y, where x and y are the lowest and highest marks, respectively. If the range and average of the marks are 70 and 64, respectively, then the ordered pair (x, y) is:​

A.

(23, 93)

B.

(35, 105)

C.

(25, 95)

D.

(30, 100)

Correct option is C

Given:

Marks: (x, 28, 35, 56, 78, 63, 65, 81, 79, 83, 80, y)

x = lowest, y = highest

Range = 70

y - x = 70

Average = 64

Formula Used:

Sum =Average×Number of observations \text{Average} \times \text{Number of observations}​​

Range = Max - Min

Solution:
total of 12 marks = 64×12=7684 \times 12 = 768​​

Sum of known 10 marks
28 + 35 + 56 + 78 + 63 + 65 + 81 + 79 + 83 + 80 = 648.
So,
x + y + 648 = 768 

x + y = 120
Also,
y - x = 70
Solve the system:
Now,

2y = 190

y = 95

x = 120 - 95 = 25.
(x, y) = (25, 95)

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