Answers

Subtract 21/42 from 20/90

20/90 - 21/42 is -5/18.

Steps for subtracting fractions

1. Find the least common denominator or LCM of the two denominators:
   LCM of 90 and 42 is 630
   
   Next, find the equivalent fraction of both fractional numbers with denominator 630
2. For the 1st fraction, since 90 × 7 = 630,
   20/90 = 20 × 7/90 × 7 = 140/630
3. Likewise, for the 2nd fraction, since 42 × 15 = 630,
   21/42 = 21 × 15/42 × 15 = 315/630
4. Subtract the two like fractions:
   140/630 - 315/630 = 140 - 315/630 = -175/630
5. After reducing the fraction, the answer is -5/18

MathStep (Works offline)

Download our mobile app and learn to work with fractions in your own time:
Android and iPhone/ iPad

Related: ⁴⁰/₉₀-²¹/₄₂ ²⁰/₉₀-²¹/₈₄ ⁶⁰/₉₀-²¹/₄₂ ²⁰/₉₀-⁶³/₄₂

Subtract Fractions Calculator