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Finding the Fourth Proportional to 685.40, 945.90 and 390.76

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Solution

The fourth proportional to 685.40, 945.90 and 390.76 is: 539.28

Step by Step Solution

  1. Step 1: Write the proportion equation
    685.40 : 945.90 = 390.76 : x
  2. Step 2: Convert to fraction form
    685.40/945.90 = 390.76/x
  3. Step 3: Cross multiply
    685.40x = 945.90 × 390.76
  4. Step 4: Simplify right side
    685.40x = 369,619.88
  5. Step 5: Solve for x
    x = 369,619.88/685.40
  6. Step 6: Final answer
    x = 539.28

Related Problems

Find fourth proportional to 342.70, 472.95 and 195.38
Half scale
Find fourth proportional to 1,370.80, 1,891.80 and 781.52
Double scale
Find fourth proportional to 686.40, 947.28 and 391.76
Similar ratio
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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.