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Finding the Fourth Proportional to 1,290.61, 1,781.90 and 991.32

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Solution

The fourth proportional to 1,290.61, 1,781.90 and 991.32 is: 1,368.68

Step by Step Solution

  1. Step 1: Write the proportion equation
    1,290.61 : 1,781.90 = 991.32 : x
  2. Step 2: Convert to fraction form
    1,290.61/1,781.90 = 991.32/x
  3. Step 3: Cross multiply
    1,290.61x = 1,781.90 × 991.32
  4. Step 4: Simplify right side
    1,290.61x = 1,766,438.45
  5. Step 5: Solve for x
    x = 1,766,438.45/1,290.61
  6. Step 6: Final answer
    x = 1,368.68

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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.