Gem left home at 11.20 a.m. and drove towards the suburb. 2 hours later, her older brother left their home and drove towards the same suburb at 86 km/h. When the older brother reached the suburb at 4.20 p.m., Gem had another 5 km to travel. What was Gem’s average speed? Express your answer in mixed number.
Time that the Gem's older brother started driving = 1.20 p.m.
Duration that Gem's older brother drove from 1.20 p.m. to 4.20 p.m. = 3 h

Distance that Gem's older brother travelled
= 3 x 86
= 258 km

Distance that Gem travelled by the time her older brother reached the city
= 258 - 5
= 253 km

Time that Gem took to travel 253 km = 5 h

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

Answer(s): 50³₅ km/h