Home / 390.40-538.78-257.56

Finding the Fourth Proportional to 390.40, 538.78 and 257.56

Calculator

Solution

The fourth proportional to 390.40, 538.78 and 257.56 is: 355.45

Step by Step Solution

  1. Step 1: Write the proportion equation
    390.40 : 538.78 = 257.56 : x
  2. Step 2: Convert to fraction form
    390.40/538.78 = 257.56/x
  3. Step 3: Cross multiply
    390.40x = 538.78 × 257.56
  4. Step 4: Simplify right side
    390.40x = 138,768.18
  5. Step 5: Solve for x
    x = 138,768.18/390.40
  6. Step 6: Final answer
    x = 355.45

Related Problems

Find fourth proportional to 195.20, 269.39 and 128.78
Half scale
Find fourth proportional to 780.80, 1,077.56 and 515.12
Double scale
Find fourth proportional to 391.40, 540.16 and 258.56
Similar ratio
Find fourth proportional to 585.60, 808.17 and 386.34
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.