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Complete Question
A 6-ft-tall person walks away from a 11-ft lamppost at a constant rate of 3.3 ft/sec. What is the rate that the tip of the person's shadow moves away from the lamppost when the person is 11 ft away from the lampost?
Answer:
7.26ft/s
Explanation:
A 6-ft-tall person walks away from a 11-ft lamppost at a constant rate of 3.3 ft/sec. What is the rate that the tip of the person's shadow moves away from the lamppost when the person is 11 ft away from the lampost?
Let x = distance of person to the tip of the lamp post
= 6/x = 11/d
Cross Multiply
6d = 11 x....... Equation 1
The constant rate of the person = 3.3 ft/s
= Distance of the person to the pole = Speed × time
= 3.3 × t
d = 3.3t
x = d - 3.3t
Substitute d - 3.3t for x in Equation 1
6d = 11x
6d = 11(d - 3.3t)
6d = 11d - 36.3t
36.3t = 11d - 6d
36.3t = 5d
d = 36.3/5
d = 7.26 ft/s