Example

Solving a Word Problem for a Car's Original Price

Apply the problem-solving strategy to find an original price when only a fractional portion of it is known, using the Multiplication Property of Equality.

Problem: Andreas purchased a used car for $12,000. Since the car was 44 years old, this price was 34\frac{3}{4} of the original price when it was new. What was the original price of the car?

  1. Identify what to find: the original price of the car when it was new.
  2. Name the unknown: Let pp = the original price.
  3. Translate into a sentence and equation: "$12,000 is 34\frac{3}{4} of the original price." This becomes the equation 12,000=34p12{,}000 = \frac{3}{4}p.
  4. Solve by multiplying both sides by 43\frac{4}{3}, the reciprocal of the fractional coefficient 34\frac{3}{4}:

43(12,000)=4334p\frac{4}{3}(12{,}000) = \frac{4}{3} \cdot \frac{3}{4}p

On the right side, 4334=1\frac{4}{3} \cdot \frac{3}{4} = 1 by the inverse property of multiplication, leaving just pp. On the left side, 4312,000=16,000\frac{4}{3} \cdot 12{,}000 = 16{,}000:

16,000=p16{,}000 = p

  1. Check by substituting back: Is 34\frac{3}{4} of $16,000 equal to $12,000?

3416,000=?12,000\frac{3}{4} \cdot 16{,}000 \stackrel{?}{=} 12{,}000

12,000=12,00012{,}000 = 12{,}000 \checkmark

  1. Answer: The original price of the car was $16,000.

This example illustrates how the phrase "fraction of a quantity" translates into multiplication by that fraction. When the known value equals a fraction times the unknown, the equation takes the form known=abp\text{known} = \frac{a}{b} \cdot p, and the unknown is isolated by multiplying both sides by the reciprocal ba\frac{b}{a}. This pattern arises frequently in real-world problems involving discounts, depreciation, or partial quantities.

0

1

Updated 2026-04-21

Tags

OpenStax

Elementary Algebra @ OpenStax

Ch.3 Math Models - Elementary Algebra @ OpenStax

Algebra

Math

Prealgebra

Related
Learn After