Let the four numbers be x, a, b, and c, with x being the first number. The average is given by \frac{x + a + b + c}{4} = 48, which implies x + a + b + c = 192. It is also given that x = \frac{1}{3}(a + b + c). Substituting this into the sum equation yields: \[x + a + b + c = 192\] Replacing (a + b + c) with 3x: \[x + 3x = 192\] This simplifies to: \[4x = 192\] Solving for x: \[x = 48\] Therefore, the first number is 48.