Problema Solution
Harriet drove for 90 miles in the city. When she got on the highway she increased her speed by 20 mph and drove for 130 miles. If Harriet drove for a total of 4 hours how fast did she drive on the highway?
Answer provided by our tutors
let
v1 = the speed in the city
v2 = v1 + 20 mph the speed on the highway
t1 = the time she drove in the city
t2 = the time she drove on the highway
d1 = 90 mi the distance she drove in the city
d2 = 130 mi the distance she drove on the highway
since speed = distance/time
v1*t1 = d1
v1*t1 = 90 divide both sides by v1
t1 = 90/v1
v2*t2 = d2
(20 + v1)*t2 = 130 divide both sides by (20 + v1)
t2 = 130/(20 + v1)
Harriet drove for a total of 4 hours
t1 + t2 = 4
plug t1 = 90/v1 and t2 = 130/(20 + v1) into the last equation
90/v1 + 130/(20 + v1) = 4
by solving we find
v1 = 45 mph
click here to see the step by step solution of the equation
v2 = 45 + 20
v2 = 65 mph
Harriet drove with 65 miles per hour on the highway.