Mary left home at 10.10 a.m. and drove towards the suburb. 3 hours later, her cousin left their home and drove towards the same suburb at 85 km/h. When the cousin reached the suburb at 6.10 p.m., Mary had another 5 km to travel. What was Mary’s average speed? Express your answer in mixed number.
Time that the Mary's cousin started driving = 1.10 p.m.
Duration that Mary's cousin drove from 1.10 p.m. to 6.10 p.m. = 5 h

Distance that Mary's cousin travelled
= 5 x 85
= 425 km

Distance that Mary travelled by the time her cousin reached the city
= 425 - 5
= 420 km

Time that Mary took to travel 420 km = 8 h

Mary's average speed
= 420 ÷ 8
= 52¹₂ km/h

Answer(s): 52¹₂ km/h