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April 21, 2014

April 21, 2014

Posted by **Sara** on Thursday, May 17, 2012 at 6:24pm.

2) Matt and Sara mow lawns together. When Matt mows the lawn for Mr. Smith it takes 100 minutes. When matt and Sara work together to mow the lawn for Smith they get the job done in 40 minutes. How long will it take Sara to mow Smith's lawn by herself?

- Math -
**Reiny**, Thursday, May 17, 2012 at 6:45pmspeed of private plane --- x mph

speed of jet -----> 3x mph

time for 1st leg of trip = 1350/x

time for 2nd leg of trip = 600/(3x) = 200/x

so 1350/x + 200/x = 6

1550/x=6

6x = 1550

x = 258.333..

private plane went 258.33 mph, jet went 775 mph

- Math -
**Reiny**, Thursday, May 17, 2012 at 6:50pmMatt's rate = lawn/100

Sara's rate = lawn/x , where x is Sara's time if she works alone

combined rate = lawn/100 + lawn/x

= (xlawn + 100lawn)/(100x)

= lawn*(x+100)/(100x)

then lawn*(x+100)/(100x) = lawn/40

(x+100)/(100x) = 1/40

cross-multiply

100x = 40x + 4000

60x = 4000

x = 66.666. or 66 2/3 minutes

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