Zara left home at 11.50 a.m. and drove towards the city. 2 hours later, her grandmother left their home and drove towards the same city at 78 km/h. When the grandmother reached the city at 6.50 p.m., Zara had another 5 km to travel. What was Zara’s average speed? Express your answer in mixed number.
Time that the Zara's grandmother started driving = 1.50 p.m.
Duration that Zara's grandmother drove from 1.50 p.m. to 6.50 p.m. = 5 h

Distance that Zara's grandmother travelled
= 5 x 78
= 390 km

Distance that Zara travelled by the time her grandmother reached the city
= 390 - 5
= 385 km

Time that Zara took to travel 385 km = 7 h

Zara's average speed
= 385 ÷ 7
= 55 km/h

Answer(s): 55 km/h