Irene left home at 11.30 a.m. and drove towards the town. 2 hours later, her younger sister left their home and drove towards the same town at 83 km/h. When the younger sister reached the town at 5.30 p.m., Irene had another 2 km to travel. What was Irene’s average speed? Express your answer in mixed number.
Time that the Irene's younger sister started driving = 1.30 p.m.
Duration that Irene's younger sister drove from 1.30 p.m. to 5.30 p.m. = 4 h

Distance that Irene's younger sister travelled
= 4 x 83
= 332 km

Distance that Irene travelled by the time her younger sister reached the city
= 332 - 2
= 330 km

Time that Irene took to travel 330 km = 6 h

Irene's average speed
= 330 ÷ 6
= 55 km/h

Answer(s): 55 km/h