A strand of DNA has the sequence GATTACA. what will the sequence of the complementary strand of DNA?

CTAATGT i believe.

Explanation:

A=T

C=G

G=C

T=A

If you replace GATTACA with these complementary parts/letters, etc. you will get your answer!

Hope this helps!

Tip: The only thing that changes when finding an RNA strand is that there is Uracil (U). So when finding a complementary RNA strand A=U while everything else is the same.