The average of four numbers is 638.4. The first three numbers are \( 216,159.8 \), 301.25. Find the fourth number.

To find the fourth number, we first need to calculate the total sum of the four numbers. Since the average of the four numbers is 638.4, we can use the formula for the average: \[ \text{Average} = \frac{\text{Sum of all numbers}}{\text{Number of numbers}} \] Rearranging gives us: \[ \text{Sum of all numbers} = \text{Average} \times \text{Number of numbers} \] Substituting the values, we have: \[ \text{Sum of all numbers} = 638.4 \times 4 = 2553.6 \] Next, we will sum the first three numbers: \[ 216 + 159.8 + 301.25 = 677.05 \] Now, we can find the fourth number by subtracting the sum of the first three numbers from the total sum: \[ \text{Fourth number} = 2553.6 - 677.05 = 1876.55 \] Thus, the fourth number is \( 1876.55 \).