Finding the Fourth Proportional to 1,261.61, 1,892.69 and 428.61

Step by Step Solution

1. Step 1: Write the proportion equation
   1,261.61 : 1,892.69 = 428.61 : x
2. Step 2: Convert to fraction form
   1,261.61/1,892.69 = 428.61/x
3. Step 3: Cross multiply
   1,261.61x = 1,892.69 × 428.61
4. Step 4: Simplify right side
   1,261.61x = 811,223.72
5. Step 5: Solve for x
   x = 811,223.72/1,261.61
6. Step 6: Final answer
   x = 643.01