Lucy left home at 10.20 a.m. and drove towards the campsite. 3 hours later, her grandmother left their home and drove towards the same campsite at 81 km/h. When the grandmother reached the campsite at 6.20 p.m., Lucy had another 3 km to travel. What was Lucy’s average speed? Express your answer in mixed number.
Time that the Lucy's grandmother started driving = 1.20 p.m.
Duration that Lucy's grandmother drove from 1.20 p.m. to 6.20 p.m. = 5 h

Distance that Lucy's grandmother travelled
= 5 x 81
= 405 km

Distance that Lucy travelled by the time her grandmother reached the city
= 405 - 3
= 402 km

Time that Lucy took to travel 402 km = 8 h

Lucy's average speed
= 402 ÷ 8
= 50¹₄ km/h

Answer(s): 50¹₄ km/h