A consumer testing service is commissioned to rank the top 3 brands of laundry detergent. A total of 10 brands are to be included in the study. In how many ways can the consumer testing service arrive at the final ranking

3x + 4y = 5 x- 3y = -7 solve by substitution

I’m still confused on how to work the percentages

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)