why is .20% equal to 1/400?

It's not. it's 1/500

Percents are always over 100.

So:

0.20% is 0.2/100

Since you have a decimal in the numerator, we want to remove it, so we multiply both halves of the fraction by 10:

2/1000

Now reduce:

1/500


1/400 would be 0.25%

Starting from 0.25%, put it over 100, like above:

0.25/100

multiply both halves by 100:

25/10000

25 is the GCF of the fraction, so divide both sides by it:

1/400

0.2%
= 0.2/100
= (0.2 x 10)/(100 x 10)
= 2/1000
= 1/500

% means per 100

per means divide

.20 divide 100 = .002

1/400 = .0025 or close enough to .002