standard_description: Understand that attributes belonging to a category of two-dimensional figures also belong to all subcategories of that category. For example, all rectangles have four right angles and squares are rectangles, so all squares have four right angles.
problem_activity: Solve.
a.
$${{7\over8}-{4\over8}}$$
b.
$${{5\over10}+{3\over10}}$$
c.
$${1-{2\over5}}$$


aligns: no