Finding the Fourth Proportional to 1,688.76, 2,531.70 and 810.72

Step by Step Solution

1. Step 1: Write the proportion equation
   1,688.76 : 2,531.70 = 810.72 : x
2. Step 2: Convert to fraction form
   1,688.76/2,531.70 = 810.72/x
3. Step 3: Cross multiply
   1,688.76x = 2,531.70 × 810.72
4. Step 4: Simplify right side
   1,688.76x = 2,052,499.82
5. Step 5: Solve for x
   x = 2,052,499.82/1,688.76
6. Step 6: Final answer
   x = 1,215.39