Yoko left home at 11.50 a.m. and drove towards the seaside resort. 2 hours later, her mother left their home and drove towards the same seaside resort at 99 km/h. When the mother reached the seaside resort at 6.50 p.m., Yoko had another 5 km to travel. What was Yoko’s average speed? Express your answer in mixed number.
Time that the Yoko's mother started driving = 1.50 p.m.
Duration that Yoko's mother drove from 1.50 p.m. to 6.50 p.m. = 5 h

Distance that Yoko's mother travelled
= 5 x 99
= 495 km

Distance that Yoko travelled by the time her mother reached the city
= 495 - 5
= 490 km

Time that Yoko took to travel 490 km = 7 h

Yoko's average speed
= 490 ÷ 7
= 70 km/h

Answer(s): 70 km/h