Barbara left home at 11.50 a.m. and drove towards the province. 2 hours later, her grandmother left their home and drove towards the same province at 87 km/h. When the grandmother reached the province at 4.50 p.m., Barbara had another 3 km to travel. What was Barbara’s average speed? Express your answer in mixed number.
Time that the Barbara's grandmother started driving = 1.50 p.m.
Duration that Barbara's grandmother drove from 1.50 p.m. to 4.50 p.m. = 3 h

Distance that Barbara's grandmother travelled
= 3 x 87
= 261 km

Distance that Barbara travelled by the time her grandmother reached the city
= 261 - 3
= 258 km

Time that Barbara took to travel 258 km = 5 h

Barbara's average speed
= 258 ÷ 5
= 51³₅ km/h

Answer(s): 51³₅ km/h