ABSTRACT
Step 1: the LCM of the two denominators; Step 2: for the fraction 13 , 3 into 21 goes 7 times,
7×the numerator is 7×1; Step 3: for the fraction 27 , 7 into 21 goes 3 times,
3×the numerator is 3×2. Thus
1 3
+ 2 7 = 7+6
21 = 13
21 as obtained previously.