Home / 21.20-31.78-20.80

Finding the Fourth Proportional to 21.20, 31.78 and 20.80

Calculator

Solution

The fourth proportional to 21.20, 31.78 and 20.80 is: 31.18

Step by Step Solution

  1. Step 1: Write the proportion equation
    21.20 : 31.78 = 20.80 : x
  2. Step 2: Convert to fraction form
    21.20/31.78 = 20.80/x
  3. Step 3: Cross multiply
    21.20x = 31.78 × 20.80
  4. Step 4: Simplify right side
    21.20x = 661.02
  5. Step 5: Solve for x
    x = 661.02/21.20
  6. Step 6: Final answer
    x = 31.18

Related Problems

Find fourth proportional to 10.60, 15.89 and 10.40
Half scale
Find fourth proportional to 42.40, 63.56 and 41.60
Double scale
Find fourth proportional to 22.20, 33.28 and 21.80
Similar ratio
Find fourth proportional to 31.80, 47.67 and 31.20
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.