Home / 428.18-642.40-139.64

Finding the Fourth Proportional to 428.18, 642.40 and 139.64

Calculator

Solution

The fourth proportional to 428.18, 642.40 and 139.64 is: 209.50

Step by Step Solution

  1. Step 1: Write the proportion equation
    428.18 : 642.40 = 139.64 : x
  2. Step 2: Convert to fraction form
    428.18/642.40 = 139.64/x
  3. Step 3: Cross multiply
    428.18x = 642.40 × 139.64
  4. Step 4: Simplify right side
    428.18x = 89,704.74
  5. Step 5: Solve for x
    x = 89,704.74/428.18
  6. Step 6: Final answer
    x = 209.50

Related Problems

Find fourth proportional to 214.09, 321.20 and 69.82
Half scale
Find fourth proportional to 856.36, 1,284.80 and 279.28
Double scale
Find fourth proportional to 429.18, 643.90 and 140.64
Similar ratio
Find fourth proportional to 642.27, 963.60 and 209.46
1.5x scale

Why These Related Problems?

These problems maintain the same ratio (1.50) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.