Subtract 18/40 from 5/21, Solve 5/21

Subtract 18/40 from 5/21

5/21 - 18/40 is -89/420.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 40 is 840

Next, find the equivalent fraction of both fractional numbers with denominator 840
For the 1st fraction, since 21 × 40 = 840,
5/21 = 5 × 40/21 × 40 = 200/840
Likewise, for the 2nd fraction, since 40 × 21 = 840,
18/40 = 18 × 21/40 × 21 = 378/840
Subtract the two like fractions:
200/840 - 378/840 = 200 - 378/840 = -178/840
After reducing the fraction, the answer is -89/420

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