Home / 40-60-21

Finding the Fourth Proportional to 40, 60 and 21

Calculator

Solution

The fourth proportional to 40, 60 and 21 is: 31.50

Step by Step Solution

  1. Step 1: Write the proportion equation
    40 : 60 = 21 : x
  2. Step 2: Convert to fraction form
    40/60 = 21/x
  3. Step 3: Cross multiply
    40x = 60 × 21
  4. Step 4: Simplify right side
    40x = 1,260
  5. Step 5: Solve for x
    x = 1,260/40
  6. Step 6: Final answer
    x = 31.50

Related Problems

Find fourth proportional to 20, 30 and 10.50
Half scale
Find fourth proportional to 80, 120 and 42
Double scale
Find fourth proportional to 41, 61.50 and 22
Similar ratio
Find fourth proportional to 60, 90 and 31.50
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.