Home / 78.90-108.90-49.40

Finding the Fourth Proportional to 78.90, 108.90 and 49.40

Calculator

Solution

The fourth proportional to 78.90, 108.90 and 49.40 is: 68.17

Step by Step Solution

  1. Step 1: Write the proportion equation
    78.90 : 108.90 = 49.40 : x
  2. Step 2: Convert to fraction form
    78.90/108.90 = 49.40/x
  3. Step 3: Cross multiply
    78.90x = 108.90 × 49.40
  4. Step 4: Simplify right side
    78.90x = 5,378.87
  5. Step 5: Solve for x
    x = 5,378.87/78.90
  6. Step 6: Final answer
    x = 68.17

Related Problems

Find fourth proportional to 39.45, 54.45 and 24.70
Half scale
Find fourth proportional to 157.80, 217.79 and 98.79
Double scale
Find fourth proportional to 79.90, 110.28 and 50.40
Similar ratio
Find fourth proportional to 118.35, 163.34 and 74.09
1.5x scale

Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.