Home / 30.78-42.21-28.89

Finding the Fourth Proportional to 30.78, 42.21 and 28.89

Calculator

Solution

The fourth proportional to 30.78, 42.21 and 28.89 is: 39.62

Step by Step Solution

  1. Step 1: Write the proportion equation
    30.78 : 42.21 = 28.89 : x
  2. Step 2: Convert to fraction form
    30.78/42.21 = 28.89/x
  3. Step 3: Cross multiply
    30.78x = 42.21 × 28.89
  4. Step 4: Simplify right side
    30.78x = 1,219.45
  5. Step 5: Solve for x
    x = 1,219.45/30.78
  6. Step 6: Final answer
    x = 39.62

Related Problems

Find fourth proportional to 15.39, 21.11 and 14.45
Half scale
Find fourth proportional to 61.56, 84.42 and 57.78
Double scale
Find fourth proportional to 31.78, 43.58 and 29.89
Similar ratio
Find fourth proportional to 46.17, 63.32 and 43.34
1.5x scale

Why These Related Problems?

These problems maintain the same ratio (1.37) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.