Solve the Proportion x/5 = 12/15 (Answer: x = 4)

Exact Answer

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Problem: Solve the Proportion x/5 = 12/15
Formula / Expression: x/5 = 12/15 → x = 4
Final Answer: x = 4
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Step-by-Step Solution:

Step 1: Set Up the Proportion Equation
Write the proportion equating the two ratios:
x / 5 = 12 / 15
Working: x/5 = 12/15

Step 2: Apply the Cross-Multiplication Property
In any true proportion A/B = C/D, the cross products are always equal: A × D = B × C.
Multiplying diagonally: (x) × (15) = (5) × (12).
Working: (x) × (15) = (5) × (12)

Step 3: Isolate the Unknown Variable x
Combine known numbers to obtain a simple one-step linear equation:
15 × x = 60.
Working: 15x = 60

Step 4: Divide to Solve for x
Divide both sides of the equation by 15:
x = 60 ÷ 15 = 4.
Working: x = 60 / 15 = 4

Step 5: Verify Proportion and Scale Multiplier
Check your work: Substituting x = 4 gives both fractions a ratio of 3x. Both fractions evaluate to the exact same value, confirming the solution is 100% correct.
Working: Check: (4 ÷ 5) = (12 ÷ 15)

Key Values:
- Solved Value (x): x = 4
- Equation: x/5 = 12/15
- Cross Product: 60
- Scale Multiplier: 3x

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Solved with FractionsCalc:
https://fractionscalc.com/solve-proportion-x-5-equals-12-15/
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x5 = 1215 → x = 4

Solved Value (x)

x = 4

Equation

x/5 = 12/15

Cross Product

Scale Multiplier

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Step-by-Step Solution: x/5 = 12/15 → x = 4

Step 1

Set Up the Proportion Equation

Write the proportion equating the two ratios:
x / 5 = 12 / 15

x/5 = 12/15

Step 2

Apply the Cross-Multiplication Property

In any true proportion A/B = C/D, the cross products are always equal: A × D = B × C.
Multiplying diagonally: (x) × (15) = (5) × (12).

(x) × (15) = (5) × (12)

Step 3

Isolate the Unknown Variable x

Combine known numbers to obtain a simple one-step linear equation:
15 × x = 60.

15x = 60

Step 4

Divide to Solve for x

Divide both sides of the equation by 15:
x = 60 ÷ 15 = 4.

x = 60 / 15 = 4

Step 5

Verify Proportion and Scale Multiplier

Check your work: Substituting x = 4 gives both fractions a ratio of 3x. Both fractions evaluate to the exact same value, confirming the solution is 100% correct.

Check: (4 ÷ 5) = (12 ÷ 15)

Visual Representation

The diagram below illustrates Solve proportion x/5 = 12/15 visually:

Summary & Alternative Representations

Property / Format	Value
Solved Value (x)	`x = 4`
Equation	`x/5 = 12/15`
Cross Product	`60`
Scale Multiplier	`3x`

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Frequently Asked Questions

How do you solve for x in the proportion x/5 = 12/15?

Cross-multiply diagonally: multiply the known diagonal pair (5 × 12 = 60) and then divide by the coefficient paired with x (15), resulting in x = 4.

What is the cross multiplication rule for proportions?

For any proportion A/B = C/D, the product of the extremes (A × D) is always equal to the product of the means (B × C).

Can a proportion have decimal answers?

Yes! If the cross-product is not evenly divisible by the coefficient, the result can be written as an exact decimal or as a simplified fraction / mixed number.