Finding the Fourth Proportional to 878.76, 1,315.71 and 810.72

Step by Step Solution

1. Step 1: Write the proportion equation
   878.76 : 1,315.71 = 810.72 : x
2. Step 2: Convert to fraction form
   878.76/1,315.71 = 810.72/x
3. Step 3: Cross multiply
   878.76x = 1,315.71 × 810.72
4. Step 4: Simplify right side
   878.76x = 1,066,672.41
5. Step 5: Solve for x
   x = 1,066,672.41/878.76
6. Step 6: Final answer
   x = 1,213.84