Given:
The average of 8 consecutive even numbers in ascending order = 17
Formula used:
Sum of the observations/Number of observations
Calculation:
Let the 8 consecutive even numbers be (2a – 6), (2a – 4), (2a – 2), 2a, (2a +2), (2a + 4), (2a + 6) and (2a + 8)
Sum of 8 consecutive even numbers = (2a – 6) + (2a – 4) + (2a – 2) + 2a, (2a +2) + (2a + 4) + (2a + 6) + (2a + 8)
⇒ 16a + (-12 +20)
⇒ 16a + 8
Average sum of 8 consecutive even numbers = (16a + 8)/8 = 17
⇒ 8(2a + 1)/8 = 17
⇒ 2a + 1 = 17
⇒ 2a = (17 – 1)
⇒ 2a = 16
Now, putting the value in last three three numbers
⇒ (2a + 4) = (16 + 4) = 20
⇒ (2a + 6) = (16 + 6) = 22
⇒ (2a + 8) = (16 + 8) = 24
Again,
Sum of last three numbers, 36 and 53 = (20 + 22 + 24 + 36 + 53)
⇒ 155
Average of sum of last three numbers, 36 and 53 = (155/5)
⇒ 31
∴ The average of the last three numbers, 36 and 53 is 31
Shortcut Trick
Concept Used:
Average consecutive even,
If the number of terms is Odd then,
Average will be the middle term of it.
If the number of terms is Even then,
Average will be the average of the middle pair.
Calculation:
According to the question,
There are 8 consecutive even numbers, which have 17 as average.
Hence the average of the middle pair is 17,
Sum of middle pair = 17 × 2 = 34
Now the pair will be,
16 + 18 = 34 (consecutive pair)
As there are 8 numbers and we have middle pair,
Then all 8 numbers will be,
10, 12, 14, 16, 18, 20, 22, 24,
Average of last 3 and 36 & 53
⇒ (20 + 22 + 24 + 36 + 53)/5 = 155/5 = 31
∴ The average of the last three numbers, 36 and 53 is 31