/usr/lib/x86_64-linux-gnu/libgmpada.so is in libgmpada5-dev 0.0.20131223-3+b1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libgmpada.so.3
/usr/lib/x86_64-linux-gnu/libgmpada.so.3