Xuan left home at 10.30 a.m. and drove towards the countryside. 3 hours later, her older brother left their home and drove towards the same countryside at 83 km/h. When the older brother reached the countryside at 6.30 p.m., Xuan had another 5 km to travel. What was Xuan’s average speed? Express your answer in mixed number.
Time that the Xuan's older brother started driving = 1.30 p.m.
Duration that Xuan's older brother drove from 1.30 p.m. to 6.30 p.m. = 5 h

Distance that Xuan's older brother travelled
= 5 x 83
= 415 km

Distance that Xuan travelled by the time her older brother reached the city
= 415 - 5
= 410 km

Time that Xuan took to travel 410 km = 8 h

Xuan's average speed
= 410 ÷ 8
= 51¹₄ km/h

Answer(s): 51¹₄ km/h