Home / 138.78-208.38-84.90

Finding the Fourth Proportional to 138.78, 208.38 and 84.90

Calculator

Solution

The fourth proportional to 138.78, 208.38 and 84.90 is: 127.48

Step by Step Solution

  1. Step 1: Write the proportion equation
    138.78 : 208.38 = 84.90 : x
  2. Step 2: Convert to fraction form
    138.78/208.38 = 84.90/x
  3. Step 3: Cross multiply
    138.78x = 208.38 × 84.90
  4. Step 4: Simplify right side
    138.78x = 17,691.46
  5. Step 5: Solve for x
    x = 17,691.46/138.78
  6. Step 6: Final answer
    x = 127.48

Related Problems

Find fourth proportional to 69.39, 104.19 and 42.45
Half scale
Find fourth proportional to 277.56, 416.76 and 169.80
Double scale
Find fourth proportional to 139.78, 209.88 and 85.90
Similar ratio
Find fourth proportional to 208.17, 312.57 and 127.35
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.