It is 1.000021
It is 1.000021 if you mean 1 and 21 millionths or 1.000020 if you mean 1 and 20 one-millionths.
Twenty one millionths in standard form is written as 0.000021. This is because each place value after the decimal point represents a power of 10 that is negative. In this case, the digit 2 is in the hundred thousandths place, the digit 1 is in the millionths place, and the rest are zeros.
0.00002
One and twenty one millionths (1.000021) in standard form is: 1.000021 × 100
Seventeen and two hundred twenty millionths (17.00022*) in standard form = 1.700022 × 101*this is the standard notation
0.000020
9.00002
.000005
396 millionths in decimal form = 0.000396
To write in 67 millionths in standard form, you would start with the digit 6, followed by a decimal point, and then the digits 7 and 0. This would be written as 6.000007 in standard form. For 68 millionths, you would write 6.000008 in standard form. This is because the millionths place is six places to the right of the decimal point.
0.000024
Eight hundred thousand and forty-two millionths in standard form is 800,000.000042