Home / 86.31-128.80-77.19

Finding the Fourth Proportional to 86.31, 128.80 and 77.19

Calculator

Solution

The fourth proportional to 86.31, 128.80 and 77.19 is: 115.19

Step by Step Solution

  1. Step 1: Write the proportion equation
    86.31 : 128.80 = 77.19 : x
  2. Step 2: Convert to fraction form
    86.31/128.80 = 77.19/x
  3. Step 3: Cross multiply
    86.31x = 128.80 × 77.19
  4. Step 4: Simplify right side
    86.31x = 9,942.07
  5. Step 5: Solve for x
    x = 9,942.07/86.31
  6. Step 6: Final answer
    x = 115.19

Related Problems

Find fourth proportional to 43.16, 64.40 and 38.60
Half scale
Find fourth proportional to 172.62, 257.60 and 154.38
Double scale
Find fourth proportional to 87.31, 130.29 and 78.19
Similar ratio
Find fourth proportional to 129.47, 193.20 and 115.79
1.5x scale

Why These Related Problems?

These problems maintain the same ratio (1.49) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.