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Out of four numbers the average of the first three is 16 and that of the last three is 15. If the last number is 20 then the first number is
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- 23
- 25
- 28
- 21
- 23
Correct Option: A
Let three numbers be a,b and c respectively.
According to question ,
Average of the first three numbers = 16
∴ a + b + c = 16 × 3 = 48 ---(i)
last number = 20
Average of the last three numbers = 15
b + c + 20 = 15 × 3 = 45
∴ b + c = 45 – 20 = 25 ---(ii)
By equation (i) - (ii), we get
a = 48 – 25 = 23
Second method to find the required answer ,
Here, n = 3, F = 16, L = 15 , l = 20, f = ?
∴ f – l = n (F – L)
f – 20 = 3 (16 – 15)
f = 3 + 20
f = 23
