Cathy left home at 11.40 a.m. and drove towards the seaside resort. 3 hours later, her auntie left their home and drove towards the same seaside resort at 81 km/h. When the auntie reached the seaside resort at 7.40 p.m., Cathy had another 3 km to travel. What was Cathy’s average speed? Express your answer in mixed number.
Time that the Cathy's auntie started driving = 2.40 p.m.
Duration that Cathy's auntie drove from 2.40 p.m. to 7.40 p.m. = 5 h

Distance that Cathy's auntie travelled
= 5 x 81
= 405 km

Distance that Cathy travelled by the time her auntie reached the city
= 405 - 3
= 402 km

Time that Cathy took to travel 402 km = 8 h

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

Answer(s): 50¹₄ km/h