SSC JE Mechanical Engineering 11 Oct 2020 Shift 1 Papers

According to the given information,
Let John's present age be "X".
8 years ago John's age was "X - 8".
After one year John's age will be "X + 1".
Here, after one year, he will be twice the age of his age 8 years ago.
So, X + 1 = 2(X - 8)
X + 1 = 2X - 16
Taking X right side,
2X - X = 1 + 16
X = 17
Hence, John's present age is "17 years".