Answer: Choice C) 2.5 mph and 12.5 mph
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Work Shown:
x = speed of slower bird
x+10 = speed of faster bird (flying 10 mph faster)
speeds are in miles per hour (mph)
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After 4 hours, the slower bird has traveled 4x miles. Let A = 4x.
After 4 hours, the faster bird has traveled 4(x+10) = 4x+40 miles. Let B = 4x+40.
The distance between them after 4 hours is A+B = 4x+4x+40 = 8x+40
Set this equal to 60, which is the given distance they are apart after 4 hours, and solve for x
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8x+40 = 60
8x+40-40 = 60-40
8x = 20
8x/8 = 20/8
x = 20/8
x = (5*4)/(2*4)
x = 5/2
x = 2.5 is the speed of the slower bird
x+10 = 2.5+10 = 12.5 is the speed of the faster bird
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After 4 hours, the bird traveling 2.5 mph travels 4*2.5 = 10 miles
After 4 hours, the bird traveling 12.5 mph travels 4*12.5 = 50 miles
This leads to a distance between them of 10+50 = 60 miles
See the attached image below.