14. Mr. Skinner can enroll 15 students per hr. Mr. Chalmer can enroll 20 students per hr. How long will it take them to enroll 140 students working together?
15. Use Unit Rates Minutes work better than hours. Mr. Skinner enrolls 15 students per 60 min., so he enrolls 15 / 60 or 1 / 4 students per min.
16. Use Unit Rates Minutes work better than hours. Mr. Chalmer enrolls 20 students per 60 min., so he enrolls 20 / 60 or 1 / 3 students per min.
17. 1 / 4 M + 1 / 3 M = 140 12( 1 / 4 M + 1 / 3 M) = 12(140) 3M + 4M = 1680 7M = 1680 M = 240 min. = 4 hrs.
19. Mrs. Krabappel can grade a set of papers in 1 1 / 2 hrs. Miss Hoover can grade them in 80 min. How long will it take them to grade one set if they both work together?
20. Use Unit Rates Minutes work better than hours. Mrs. Krabappel grades 1 / 90 of a set per min.
21. Use Unit Rates Miss Hoover grades 1 / 80 of a set per min.
22. 1 / 90 M + 1 / 80 M = 1 720( 1 / 90 M + 1 / 80 M) = 720(1) 8M + 9M = 720 17M = 720 M = 42 6 / 17 min.