Question 3 20 pts Rosa can clean a house in 7 hours When Ros

Question 3: 20 pts Rosa can clean a house in 7 hours. When Rosa and Amy work together, they can clean a house in about 4.2 hours. About how long will it take Amy to clean a house if she works by herself? 11 h 9.5 h 10 h 10.5 h 0/20 Question 4: 20 pts A barge travels at an average of 7 miles per hour in still water. The barge travels 50 miles up the Mississippi River and 50 miles down the river in a total of 17.5 hours. What is the average speed of the current in miles per hour in this section of the Mississippi River? 10 milh 3 m/h 4 m/h 2 mih 0 20

Solution

1) Let Amy take x hrs to clean house alone.

Rosa takes 7 hrs

Together they take : 1/7 + 1/x = 1/4.2

1/x = 1/4.2 - 1/7 = 0.0952

x = 10.5 hrs

2) Barge speed in still water = 7mph

Let the speed be x mph

d = 50 miles

So, 50/(7+x) + 50/( 7 -x) = 17.5

50[14]/(49 - x^2) = 17.5

49 - x^2 = 40

x = sqrt(9) = 3 mph