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Please Help me!!!

1.Sally can paint a room in 6 hours while it takes Steve 8 hours to paint the same room. How long would it take them to paint the room if they worked​ together?

2.Three postal workers can sort a stack of mail in 30 ​minutes, 45​minutes, and 90 minutes, respectively. Find how long it takes them to sort the mail if all three work together.

3.Mattie Evans drove 100 miles in the same amount of time that it took a turbopropeller plane to travel 460460 miles. The speed of the plane was 180180 mph faster than the speed of the car. Find the speed of the plane.

4.The speed of a river current is 5 mph. If a boat travels 20 miles downstream in the same time that it takes to travel 10 miles​ upstream, find the speed of the boat in still water.

5.One hose can fill a goldfish pond in 24minutes, and two hoses can fill the same pond in 15minutes. Find how long it takes the second hose alone to fill the pond.

6.A plane flies 495miles with the wind and 440 miles against the wind in the same length of time. If the speed of the wind is 10 ​mph, find the speed of the plane in still air.

Respuesta :

chandlerecole
1. - In (h) hours, sally can do h/7 of the room
    - In (h) hours, Steve can do h/8 of the room

so together to do the one room...

h/7 + h/8 = 1
8h/56 + 7h/56 = 1
8h + 7h = 56
15h = 56
h = 3.73 hours
 
Together, they can paint the room in 3.73 hours


3.  Let x be the speed of the car: 
440/100 = (x + 170)/x 
cross-multiply: 
440x = 100(x + 170) 
440x = 100x + 17,000 
340x = 17,000 
x = 17,000/340 = 50 mi/hr 
Aircraft speed = x + 170 = 220 mi/hr 


4.) Let B be the boat speed
(B + 5) x T = 20
(B - 5) x T = 10
2 x (B - 5) = B + 5
2B - 10 = B+5
B = 15 mph

That is all I know, hopefully that gets you somewhere. Sorry that I couldn't answer all of them :)