Addition Strategies by Making Ten
Let's find the number which should be added to 6 to make a 10.
6 + ? = 10
To find the required addend, let’s consider a model with 10 blocks and fill it with 6 balls.

 
Here, notice that we need four more balls to fill all the 10 blocks.
 

 
6 + 4 = 10
 
So, the required addend is 4.
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.
 
               
                 
                     
                    