Explain how you know which coins could be used to show 0.77 of a dollar
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Normal-travel DATA:
distance = 240 km
rate = x km/h
time = d/r
= 240/x hrs
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Bad weather DATA:
distance = 240 km
rate = (x-20) km/h
time = 240/(x-20) hrs
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Bad time - normal time = 2 hrs
240/(x-20) - 240/x = 2
120/(x-20) - 120/x = 1
120x -120(x-20) = x(x-20)
20 = x^2 -20x
x^2 - 20x - 20 = 0
x = [20 +- sqrt(20^2 - 4*1*-20)]/2
x = [20 +- sqrt(480)]/2
x = [20 +- 4sqrt(30)]/2
x = 10 +- 2sqrt(30)