Answer:
16 mph
Step-by-step explanation:
You should first form equations related to this information
Given,Tamara can go 4 mph faster than her sister, Samantha
Lets take speed to ride a bike for Samantha to be= x mph
The speed to ride a bike for Tamara will be= x+4 mph
To cover a distance of 80 miles, Samantha takes 1 hour longer than Tamara
Introduce the formula for time; time=distance/speed=D/S where D is distance in miles and S is speed in miles per hour
Here time Samantha takes to cover a distance of 80 miles is 1 hour more than that taken by Tamara, hence
Time taken by Samantha
[tex]=\frac{80}{x}[/tex]
Time taken by Tamara
[tex]=\frac{80}{4+x}[/tex]
Equation for difference in time
[tex]=\frac{80}{x} -\frac{80}{4+x} =1[/tex]
Solve the equation for difference in time to get value of x which is samantha speed
[tex]=\frac{80}{x} -\frac{80}{x+4} =1\\\\\\=80(4+x)-80(x)=x(4+x)\\\\\\=320+80x-80x=4x+x^2\\\\\\=x^2+4x-320=0[/tex]
Solve quadratic equation by the quadratic formula where a=1,b=4 and c=-320
x=(-b±√b²-4ac)÷2a
x=(-4±√4²-4×1×-320)÷2×1
[tex]x=\frac{-4+/-\sqrt{4^2-4*1*-320} }{2} \\\\\\x=(-4+/-\sqrt{1296} )/2\\\\\\x=\frac{-4+36}{2} =\frac{32}{2} =16[/tex]
Samantha speed is 16 mph
