Cathy left home at 11.30 a.m. and drove towards the city. 3 hours later, her grandfather left their home and drove towards the same city at 99 km/h. When the grandfather reached the city at 7.30 p.m., Cathy had another 5 km to travel. What was Cathy’s average speed? Express your answer in mixed number.
Time that the Cathy's grandfather started driving = 2.30 p.m.
Duration that Cathy's grandfather drove from 2.30 p.m. to 7.30 p.m. = 5 h

Distance that Cathy's grandfather travelled
= 5 x 99
= 495 km

Distance that Cathy travelled by the time her grandfather reached the city
= 495 - 5
= 490 km

Time that Cathy took to travel 490 km = 8 h

Cathy's average speed
= 490 ÷ 8
= 61¹₄ km/h

Answer(s): 61¹₄ km/h