Winnie left home at 11.50 a.m. and drove towards the town. 2 hours later, her younger brother left their home and drove towards the same town at 91 km/h. When the younger brother reached the town at 4.50 p.m., Winnie had another 2 km to travel. What was Winnie’s average speed? Express your answer in mixed number.
Time that the Winnie's younger brother started driving = 1.50 p.m.
Duration that Winnie's younger brother drove from 1.50 p.m. to 4.50 p.m. = 3 h

Distance that Winnie's younger brother travelled
= 3 x 91
= 273 km

Distance that Winnie travelled by the time her younger brother reached the city
= 273 - 2
= 271 km

Time that Winnie took to travel 271 km = 5 h

Winnie's average speed
= 271 ÷ 5
= 54¹₅ km/h

Answer(s): 54¹₅ km/h