Home / 81.20-121.80-77.60

Finding the Fourth Proportional to 81.20, 121.80 and 77.60

Calculator

Solution

The fourth proportional to 81.20, 121.80 and 77.60 is: 116.40

Step by Step Solution

  1. Step 1: Write the proportion equation
    81.20 : 121.80 = 77.60 : x
  2. Step 2: Convert to fraction form
    81.20/121.80 = 77.60/x
  3. Step 3: Cross multiply
    81.20x = 121.80 × 77.60
  4. Step 4: Simplify right side
    81.20x = 9,451.68
  5. Step 5: Solve for x
    x = 9,451.68/81.20
  6. Step 6: Final answer
    x = 116.40

Related Problems

Find fourth proportional to 40.60, 60.90 and 38.80
Half scale
Find fourth proportional to 162.40, 243.60 and 155.20
Double scale
Find fourth proportional to 82.20, 123.30 and 78.60
Similar ratio
Find fourth proportional to 121.80, 182.70 and 116.40
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.