Home / 858.60-1,287.90-639.90

Finding the Fourth Proportional to 858.60, 1,287.90 and 639.90

Calculator

Solution

The fourth proportional to 858.60, 1,287.90 and 639.90 is: 959.85

Step by Step Solution

  1. Step 1: Write the proportion equation
    858.60 : 1,287.90 = 639.90 : x
  2. Step 2: Convert to fraction form
    858.60/1,287.90 = 639.90/x
  3. Step 3: Cross multiply
    858.60x = 1,287.90 × 639.90
  4. Step 4: Simplify right side
    858.60x = 824,127.21
  5. Step 5: Solve for x
    x = 824,127.21/858.60
  6. Step 6: Final answer
    x = 959.85

Related Problems

Find fourth proportional to 429.30, 643.95 and 319.95
Half scale
Find fourth proportional to 1,717.20, 2,575.80 and 1,279.80
Double scale
Find fourth proportional to 859.60, 1,289.40 and 640.90
Similar ratio
Find fourth proportional to 1,287.90, 1,931.85 and 959.85
1.5x scale

Why These Related Problems?

These problems maintain the same ratio (1.50) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.