Question

Kelli swam upstream for some distance in one hour. she then swam downstream the same river for the same distance in only 6 minutes. if the river flows at 5 km/hr, how fast can kelli swim in still water? choose the most logical value for the variable to represent. let x = .

Answers

  1. Kelli can swim at the speed of 55/9 km/hr., that is, x = 55/9 km/hr.
    Formulas to know:
    • Speed = Distance/Time
    • Time = Distance/Speed
    • Distance = Speed*Time.
    We assume Kelli’s speed to be x km/hr.
    The speed of the river is given to be 5 km/hr.
    Thus, Kelli’s speed, swimming upstream = (x – 5) km/hr.
    Kelli’s speed, swimming downstream = (x + 5) km/hr.
    Kelli’s time swimming upstream = 1 hour.
    Kelli’s time swimming downstream = 6 minutes = 6/60 hours = 1/10 hours.
    Thus, Kelli’s distance swimming upstream = 1(x – 5) km. = (x – 5) km.
    Kelli’s distance swimming downstream = (1/10)(x + 5) km.
    But, the distance in both cases is constant.
    Thus, we get the equation:
    (x – 5) = (1/10)(x + 5),
    or, 10x – 50 = x + 5,
    or, 10x – x = 50 + 5,
    or, 9x = 55,
    or, x = 55/9.
    Thus, Kelli can swim at the speed of 55/9 km/hr., that is, x = 55/9 km/hr.
    Learn more about the upstream and downstream speed at
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