Pre-Algebra Intro fractionsmixed numbers

Mixed Numbers & Improper Fractions

Converting between the two forms, and which one to use when.

Video by Khan Academy — “Converting mixed numbers to improper fractions | Fractions | Pre-Algebra | Khan Academy” Watch on YouTube

The explanation

Key idea Mixed numbers read better; improper fractions calculate better.

2 3/4 and 11/4 are the same amount. The mixed number is easier to picture, the improper fraction is easier to compute with.

To go from mixed to improper: multiply the whole number by the denominator and add the numerator. For 2 3/4: 2 × 4 = 8, plus 3 = 11, so 11/4.

To go back: divide. 11 ÷ 4 = 2 remainder 3, so 2 3/4.

Rule of thumb: convert to improper before multiplying or dividing, always. Doing it any other way invites mistakes.

Worked example

Compute 3 1/2 × 1 3/5.

  1. Convert: 3 1/2 = 7/2 and 1 3/5 = 8/5.
  2. Multiply: 7/2 × 8/5 = 56/10.
  3. Simplify: 28/5.
  4. Convert back if asked: 5 3/5.

Answer: 28/5 or 5 3/5

Common mistakes

  • Multiplying mixed numbers by multiplying whole parts and fraction parts separately.
  • Adding instead of multiplying in the conversion: 2 3/4 becomes 11/4, not 9/4.