Risa left home at 11.35 a.m. and drove towards the campsite. 2 hours later, her grandmother left their home and drove towards the same campsite at 83 km/h. When the grandmother reached the campsite at 5.35 p.m., Risa had another 5 km to travel. What was Risa’s average speed? Express your answer in mixed number.
Time that the Risa's grandmother started driving = 1.35 p.m.
Duration that Risa's grandmother drove from 1.35 p.m. to 5.35 p.m. = 4 h

Distance that Risa's grandmother travelled
= 4 x 83
= 332 km

Distance that Risa travelled by the time her grandmother reached the city
= 332 - 5
= 327 km

Time that Risa took to travel 327 km = 6 h

Risa's average speed
= 327 ÷ 6
= 54¹₂ km/h

Answer(s): 54¹₂ km/h