# Related rates

A man starts walking north at 4 ft/s from a point P. Five minutes later a woman starts walking south at 5 ft/s from a point 500 ft due east of P. At what rate are the people moving apart 15 min after the woman starts walking?

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#### Solution Preview

After the first 5 minutes, the man has walked 4*60*5=1200 ft

the man's distance from P is a=1200+4t, where t is the time after the woman starts walking. And da/dt=4

and the woman's distance from P is ...

#### Solution Summary

This show show to find the rate of change of distance between two people.

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