Subtract 20/21 from 18/40
18/40 - 20/21 is -211/420.
Steps for subtracting fractions
- Find the least common denominator or LCM of the two denominators:
LCM of 40 and 21 is 840
Next, find the equivalent fraction of both fractional numbers with denominator 840 - For the 1st fraction, since 40 × 21 = 840,
18/40 = 18 × 21/40 × 21 = 378/840 - Likewise, for the 2nd fraction, since 21 × 40 = 840,
20/21 = 20 × 40/21 × 40 = 800/840 - Subtract the two like fractions:
378/840 - 800/840 = 378 - 800/840 = -422/840 - After reducing the fraction, the answer is -211/420
MathStep (Works offline)
Download our mobile app and learn to work with fractions in your own time:
Android and iPhone/ iPad
Related: 36/40-20/21 18/40-40/21 18/80-20/21 18/40-20/42 54/40-20/21 18/40-60/21 18/40-20/63 90/40-20/21