Home / 85.65-128.25-81.18

Finding the Fourth Proportional to 85.65, 128.25 and 81.18

Calculator

Solution

The fourth proportional to 85.65, 128.25 and 81.18 is: 121.56

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.65 : 128.25 = 81.18 : x
  2. Step 2: Convert to fraction form
    85.65/128.25 = 81.18/x
  3. Step 3: Cross multiply
    85.65x = 128.25 × 81.18
  4. Step 4: Simplify right side
    85.65x = 10,411.34
  5. Step 5: Solve for x
    x = 10,411.34/85.65
  6. Step 6: Final answer
    x = 121.56

Related Problems

Find fourth proportional to 42.83, 64.13 and 40.59
Half scale
Find fourth proportional to 171.30, 256.50 and 162.36
Double scale
Find fourth proportional to 86.65, 129.75 and 82.18
Similar ratio
Find fourth proportional to 128.48, 192.38 and 121.77
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.