Question

ulie drives 90 mi to Grandmother's house. On the way to Grandmother's, Julie drives half the distance at 30 mph and half the distance at 60 mph . On her return trip, she drives half the time at 30 mph and half the time at 60 mph .

Answer 1

for first half distance :

v = speed = 30 mph

d = distanc = 90/2 = 45 mi

time taken = t = d/v = 45/30 = 1.5 h

for second half distance :

v = speed = 60 mph

d = distanc = 90/2 = 45 mi

time taken = t = d/v = 45/60 = 0.75 h

On return trip :

for first half distance :

v = speed = 30 mph

d = distanc = 90/2 = 45 mi

time taken = t = d/v = 45/30 = 1.5 h

for second half distance :

v = speed = 60 mph

d = distanc = 90/2 = 45 mi

time taken = t = d/v = 45/60 = 0.75 h

T = total time taken = 1.5 + 0.75 + 1.5 + 0.75 = 4.5 h

D = total distance = 90 + 90 = 180 mi

average speed is given as

V_avg = D/T = 180/4.5 = 40 mph