Finding the Fourth Proportional to 1,428.32, 2,139.16 and 1,388.91

Step by Step Solution

1. Step 1: Write the proportion equation
   1,428.32 : 2,139.16 = 1,388.91 : x
2. Step 2: Convert to fraction form
   1,428.32/2,139.16 = 1,388.91/x
3. Step 3: Cross multiply
   1,428.32x = 2,139.16 × 1,388.91
4. Step 4: Simplify right side
   1,428.32x = 2,971,093.77
5. Step 5: Solve for x
   x = 2,971,093.77/1,428.32
6. Step 6: Final answer
   x = 2,080.13