A boy runs to a shopping mall and comes back in 15 minutes. his speed on the way to the mall is 5 metre per second and his speed on the way back is 4 metre per second. find the distance to the mall.

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Solution

To the mall DATA:
rate = 5 m/s ; distance = x meters ; time = d/r = x/5 meters/second
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From the mall DATA:
rate = 4 m/s ; distance = x meters ; time = d/r = x/4 meters/second
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Equation:
time + time = 15 minutes=900 seconds
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x/5 + x/4 = 900
4x + 5x = 20900
9x = 20900
x = 2000 meters

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