Home / 390-509

Finding the Third Proportional to 390 and 509

Calculator

Solution

The third proportional to 390 and 509 is: 664.31

Step by Step Solution

  1. Step 1: Write the proportion equation
    390 : 509 = 509 : x
  2. Step 2: Convert to fraction form
    390/509 = 509/x
  3. Step 3: Cross multiply
    390x = 509 × 509
  4. Step 4: Simplify right side
    390x = 259,081
  5. Step 5: Solve for x
    x = 259,081/390
  6. Step 6: Final answer
    x = 664.31

Related Problems

Find third proportional to 195 and 254.50
Half scale
Find third proportional to 780 and 1,018
Double scale
Find third proportional to 392 and 512
Similar ratio
Find third proportional to 585 and 763.50
1.5x scale

Why These Related Problems?

These problems maintain the same ratio (1.31) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.