these quantities are related by TIME

we need expressions for how distance, speed and time are related.

distance travelled is: d

average speed = (distance)/(time)

so time to travel distance is:

time = distance/average speed.

when average speed is x, time is t1:

t1 = d/x (eq.1)

when average speed is y, time is t2:

t2 = d/y (eq. 2)

overall the average speed is 50 mph:

50 = (total distance)/(total time) = (2d)/(t1 + t2)

(eq.3)

subsitute t1 and t2 from the first two equations (eq.1) and (eq.2) into (eq.3).

this gives: 50 = (2d)/(d/x + d/y)

…solve for y

g.l.

d