Thomas has constant speeds for both running and walking. When a down-escalator is moving, Thomas can run down it in 15
seconds or walk down it in
30
seconds. One day, when the escalator was broken (and stationary), it took Thomas
20
seconds to run down it.

How long, in seconds, would it take Thomas to walk down the broken escalator?

Anew test for ra is being developed. the test is administered to 750 patients with ra and 750 without ra. for the sake of the question, assume the prevalence of ra in this population is 50%. of the 750 patients with ra, 575 have a positive result. of the 750 patients without ra, 150 have a positive result. what is the positive predictive value of the new test? a575/(575+150) b. 600/(600+ 150) c. 575/(575+125) d. 600/(600+ 125)