Home / 20.50-30.80-12.90

Finding the Fourth Proportional to 20.50, 30.80 and 12.90

Calculator

Solution

The fourth proportional to 20.50, 30.80 and 12.90 is: 19.39

Step by Step Solution

  1. Step 1: Write the proportion equation
    20.50 : 30.80 = 12.90 : x
  2. Step 2: Convert to fraction form
    20.50/30.80 = 12.90/x
  3. Step 3: Cross multiply
    20.50x = 30.80 × 12.90
  4. Step 4: Simplify right side
    20.50x = 397.47
  5. Step 5: Solve for x
    x = 397.47/20.50
  6. Step 6: Final answer
    x = 19.39

Related Problems

Find fourth proportional to 10.25, 15.40 and 6.45
Half scale
Find fourth proportional to 41.00, 61.61 and 25.81
Double scale
Find fourth proportional to 21.50, 32.31 and 13.90
Similar ratio
Find fourth proportional to 30.75, 46.20 and 19.36
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.