- I, II and III
- I and II
- I and III
- II and III
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.