To write a mixed number as a decimal,
1) Convert the fractional part of the mixed number to a decimal.
2) Then, place the whole number part to the left of the decimal point.
The whole number part in the mixed number will be the same as the whole number part in the decimal.
We can multiply the denominator, 20, by 5 to get 100.

= 

= 

Observe that there are two zeros in the denominator.
So, counting from right to left, place the decimal point in the numerator after two digits.
Here, as the numerator has one digit, so we add a zero to the left of the numerator.
0.05
So, 

= 

=  0.05 
Now, place the whole number part, 2, to the left of the decimal point.
2.05
So, 2 

=  2.05 
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The correct answer is
The smallest number is the one that comes first while counting.
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.