We have the number: twenty-one and twelve thousandths.
We have that twenty-one is simply 21.
However, we need to represent twelve-thousandths having into account that we need to divide that number by 1000 (we have thousandths), that is:
[tex]\frac{12}{1000}=0.012[/tex]Then, the number, in standard form, is:
21 + 0.012 = 21.012
Therefore, the number is 21.012 (in standard form, three decimals.) (option D)
