Joelle left home at 11.20 a.m. and drove towards the suburb. 2 hours later, her grandfather left their home and drove towards the same suburb at 97 km/h. When the grandfather reached the suburb at 6.20 p.m., Joelle had another 2 km to travel. What was Joelle’s average speed? Express your answer in mixed number.
Time that the Joelle's grandfather started driving = 1.20 p.m.
Duration that Joelle's grandfather drove from 1.20 p.m. to 6.20 p.m. = 5 h

Distance that Joelle's grandfather travelled
= 5 x 97
= 485 km

Distance that Joelle travelled by the time her grandfather reached the city
= 485 - 2
= 483 km

Time that Joelle took to travel 483 km = 7 h

Joelle's average speed
= 483 ÷ 7
= 69 km/h

Answer(s): 69 km/h