Fill in the blank: A student earned a grade of 80% on a math test that had 20 problems. The student answered questions correctly on the math test. (Write the number only.) *

In isosceles right triangle $abc$, point $d$ is on hypotenuse $\overline{bc}$ such that $\overline{ad}$ is an altitude of $\triangle abc$ and $dc = 5$. what is the area of triangle $abc$?