Sarah left home at 11.50 a.m. and drove towards the suburb. 2 hours later, her mother left their home and drove towards the same suburb at 86 km/h. When the mother reached the suburb at 4.50 p.m., Sarah had another 5 km to travel. What was Sarah’s average speed? Express your answer in mixed number.
Time that the Sarah's mother started driving = 1.50 p.m.
Duration that Sarah's mother drove from 1.50 p.m. to 4.50 p.m. = 3 h

Distance that Sarah's mother travelled
= 3 x 86
= 258 km

Distance that Sarah travelled by the time her mother reached the city
= 258 - 5
= 253 km

Time that Sarah took to travel 253 km = 5 h

Sarah's average speed
= 253 ÷ 5
= 50³₅ km/h

Answer(s): 50³₅ km/h