Home / 399-640

Finding the Third Proportional to 399 and 640

Calculator

Solution

The third proportional to 399 and 640 is: 1,026.57

Step by Step Solution

  1. Step 1: Write the proportion equation
    399 : 640 = 640 : x
  2. Step 2: Convert to fraction form
    399/640 = 640/x
  3. Step 3: Cross multiply
    399x = 640 × 640
  4. Step 4: Simplify right side
    399x = 409,600
  5. Step 5: Solve for x
    x = 409,600/399
  6. Step 6: Final answer
    x = 1,026.57

Related Problems

Find third proportional to 199.50 and 320
Half scale
Find third proportional to 798 and 1,280
Double scale
Find third proportional to 401 and 643
Similar ratio
Find third proportional to 598.50 and 960
1.5x scale

Why These Related Problems?

These problems maintain the same ratio (1.60) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.