If you want a percent as a decimal so you can divide you must make it a decimal for example in your case it would be like this, 0.05, then all you do is divide 1,000 by 0.05
Adenine pairs with Thymine and Guanine pairs with Cytosine. I remember this by the car (C) goes in the garage (G). Then A and T are the only ones left, so they pair together.