Home / 138.78-207.90-90.72

Finding the Fourth Proportional to 138.78, 207.90 and 90.72

Calculator

Solution

The fourth proportional to 138.78, 207.90 and 90.72 is: 135.90

Step by Step Solution

  1. Step 1: Write the proportion equation
    138.78 : 207.90 = 90.72 : x
  2. Step 2: Convert to fraction form
    138.78/207.90 = 90.72/x
  3. Step 3: Cross multiply
    138.78x = 207.90 × 90.72
  4. Step 4: Simplify right side
    138.78x = 18,860.69
  5. Step 5: Solve for x
    x = 18,860.69/138.78
  6. Step 6: Final answer
    x = 135.90

Related Problems

Find fourth proportional to 69.39, 103.95 and 45.36
Half scale
Find fourth proportional to 277.56, 415.80 and 181.44
Double scale
Find fourth proportional to 139.78, 209.40 and 91.72
Similar ratio
Find fourth proportional to 208.17, 311.85 and 136.08
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.