Home / 139.78-209.65-85.66

Finding the Fourth Proportional to 139.78, 209.65 and 85.66

Calculator

Solution

The fourth proportional to 139.78, 209.65 and 85.66 is: 128.48

Step by Step Solution

  1. Step 1: Write the proportion equation
    139.78 : 209.65 = 85.66 : x
  2. Step 2: Convert to fraction form
    139.78/209.65 = 85.66/x
  3. Step 3: Cross multiply
    139.78x = 209.65 × 85.66
  4. Step 4: Simplify right side
    139.78x = 17,958.62
  5. Step 5: Solve for x
    x = 17,958.62/139.78
  6. Step 6: Final answer
    x = 128.48

Related Problems

Find fourth proportional to 69.89, 104.83 and 42.83
Half scale
Find fourth proportional to 279.56, 419.30 and 171.32
Double scale
Find fourth proportional to 140.78, 211.15 and 86.66
Similar ratio
Find fourth proportional to 209.67, 314.48 and 128.49
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.