Add and Subtract Like Fractions
To add (or subtract) like fractions, add (or subtract) the numerators, and put the result over the common denominator.
For example, let's find the sum:

+ 

Observe that the denominator is same in both the fractions.
So, add the numerators, and put the obtained result over the common denominator.

+ 

= 

= 

Now, simplify:

= 

= 

So, 

+ 

= 

. 
ds
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Help
The correct answer is
Remember :
The smallest number is the one that comes first while counting.
Solution :
To arrange the given numbers in order from smallest to greatest, find the smallest number among all the given numbers.
21,27,23
21 is the smallest number.