This one twelve less one fourth of a number

The? half-life of a radioactive substance is 20 years. if you start with some amount of this? substance, what fraction will remain in 120 ? years

Ahyperbola centered at the origin has a vertex at (-6,0) and a focus at (10,0)

Calculate the mean value (expected value) of the following discrete variable x (10 points): x = 0, 1, 2, 3, 4, 5, 6 p(x) = 0.2, 0.2, 0.15, 0.15, 0.15, 0.1, 0.05