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Malik walked up and back down an empty 
18m long escalator at a constant rate. Since the escalator was going up at the time, it took him only 
22.5s. Going down took Malik 
90s. Assume the escalator speed is constant.
What was Malik's walking speed?

(m)/(s)

Malik walked up and back down an empty 18 m 18 \mathrm{~m} long escalator at a constant rate. Since the escalator was going up at the time, it took him only 22.5 s 22.5 \mathrm{~s} . Going down took Malik 9090 s. Assume the escalator speed is constant.\newlineWhat was Malik's walking speed?\newlinems \frac{\mathrm{m}}{\mathrm{s}}

Full solution

Q. Malik walked up and back down an empty 18 m 18 \mathrm{~m} long escalator at a constant rate. Since the escalator was going up at the time, it took him only 22.5 s 22.5 \mathrm{~s} . Going down took Malik 9090 s. Assume the escalator speed is constant.\newlineWhat was Malik's walking speed?\newlinems \frac{\mathrm{m}}{\mathrm{s}}
  1. Define variables: Define the variables for Malik's walking speed and the escalator speed.\newlineLet's denote Malik's walking speed as vm v_m (in meters per second) and the escalator speed as ve v_e (in meters per second).
  2. Set up equations: Set up the equations based on the given information.\newlineWhen Malik is going up, the escalator's speed adds to his walking speed, so the total speed is vm+ve v_m + v_e . It takes him 2222.55 seconds to cover the 1818 meters, so we have the equation:\newline18=(vm+ve)×22.5 18 = (v_m + v_e) \times 22.5 \newlineWhen going down, the escalator's speed subtracts from his walking speed, so the total speed is vmve v_m - v_e . It takes him 9090 seconds to cover the same distance, so we have the equation:\newline18=(vmve)×90 18 = (v_m - v_e) \times 90
  3. Solve first equation: Solve the first equation for vm+ve v_m + v_e .\newlinevm+ve=1822.5 v_m + v_e = \frac{18}{22.5} \newlineCalculate the right side of the equation.\newlinevm+ve=0.8 v_m + v_e = 0.8 m/s
  4. Solve second equation: Solve the second equation for vmve v_m - v_e .\newlinevmve=1890 v_m - v_e = \frac{18}{90} \newlineCalculate the right side of the equation.\newlinevmve=0.2 v_m - v_e = 0.2 m/s
  5. Add equations: Add the two equations to solve for Malik's walking speed vm v_m .\newline(vm+ve)+(vmve)=0.8+0.2 (v_m + v_e) + (v_m - v_e) = 0.8 + 0.2 \newline2vm=1.0 2v_m = 1.0 \newlineNow, divide both sides by 22 to find vm v_m .\newlinevm=1.02 v_m = \frac{1.0}{2} \newlineCalculate the value of vm v_m .\newlinevm=0.5 v_m = 0.5 m/s

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