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Option 4 : II and III

Given:

Average of 15 numbers = 60

Average of the first seven numbers = 63

Average of next five numbers = 59

15th number = 1/2(13th number)

14th number = 4 + 15th number

Formula Used:

Average = Sum of values/Number of values

Calculation:

Let 13th, 14th, and 15th numbers are a, b, and c

c = a/2

b = 4 + c

⇒ 4 + a/2

Sum of the first seven numbers/7 = 63

⇒ Sum of the first seven numbers = 441

Sum of the next five numbers/5 = 59

⇒ Sum of the next five numbers = 295

Sum of 15 numbers/15 = 60

⇒ Sum of 15 numbers = 900

⇒ 441 + 295 + a + b + c = 900

⇒ 736 + a + b + c = 900

⇒ a + b + c = 164

⇒ a + 4 + a/2 + a/2 = 164

⇒ 2a = 160

⇒ a = 80

⇒ c = 40

⇒ b = 44

I. Average of the last three numbers is an integer

(80 + 44 + 40)/3 = 164/3

⇒ 54.67

This is not an integer.

⇒ I is not correct

II. Fourteenth number is divisible by 11

44 = 4 × 11

⇒ II is correct

III. Average of 13th and 15th number is not 65

(80 + 40)/2 = 120/2

⇒ 60

⇒ III is correct

∴ II and III are correct.

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