In a certain population 95% of the population does not have…

In a certain population 95% of the population does not have a certain STD. A medical test has been devised that detects the STD 90% of the time in individuals who have the STD. The test also confirms that individuals who do not have the STD correctly 85% of the time. What is the probability an individual has an STD and tests positive?

Rust has the formula Fe2O3 and it’s made from iron metal rea…

Rust has the formula Fe2O3 and it’s made from iron metal reacting with oxygen over time.  Assume you had a 2.0 g block of pure iron metal that fully oxidized to rust and the mass of that rust product was 6.5 g.  What must have been the mass of oxygen initially reacting with the pure iron?   *give numerical answer, no unit required