Of the four numbers, whose average is 80, the first is one-fourth of the sum of the last three. What is the value of the first number?

Question: Of the four numbers, whose average is 80, the first is one-fourth of the sum of the last three. What is the value of the first number?

Solution:
Average of four numbers is 80
The sum of four numbers is = (4 × 80) = 320

let, the first number is x
then sum of last three is 4x

x + 4x = 320
⇒ 5x = 320
∴ x = 64