The half life of a certain substance is 21 years. How long will it take for a sample of this substance to decay to 88% of its original amount?

Identify the translation rule on a coordinate plane that verifies that square a(-4, 3), b(-4, 8), c(-9, 3), d(-9, 8) and square a'(-3, 2), b'(-3, 7), c'(-8, 2), d'(-8, 7) are congruent.

The rows and columns of lattice points in a three-by-three square array are evenly spaced one unit apart. how many distinct triangles with at least one side of length 2 units can be drawn using three lattice points for the vertices?

John bought 5 lemons and used 2 of them for a salad how much did he use for.a salad . he used % of the lemons.