Out of 6 numbers, the sum of the first 5 numbers is 11 times the sixth number. If the average of the 6 numbers is 144, what is the sixth number?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 72
The sum of all the numbers is the average multiplied by how many numbers there are. Writing the first five in terms of the sixth turns that sum into a single unknown.
Sum of the 6 numbers \(=6\times144=864\)
Let the sixth number be \(x\); the sum of the first five \(=11x\)
\(11x+x=12x=864\)
\(\displaystyle x=\frac{864}{12}=72\)
The sixth number is 72.