Question 191642
    Andrea can rake her Dad's yard in 45 minutes. Andrea's brother Bradford rakes one and one-half times faster than Andrea. How long would it take them to rake their Dad's yard together?
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Andrea's rate:
1 job per 45 minutes
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Brother's rate:
1.5x = 45 
x = 45/1.5
x = 1 job per 30 minutes
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Let t = time (in hours) it would take for them to work together
then
(1/45)t + (1/30)t = 1
30t + 45t = 1350
75t = 1350
t = 1350/75
t = 18 minutes