Which situation represents a proportional relationship?

A car used 3 gallons of gas to drive 72 miles on a
highway and used 4 gallons of gas to drive 72 miles
in town.

A store charged $20 for 2 shirts and charged $25 for
3 shirts.

An alarm on a clock beeped 7 times in 6 seconds
and beeped 14 times in 12 seconds.

A signal light flashed yellow 7 times in 28 seconds
and flashed red 5 times in 35 seconds.

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)