Diana left home at 11.45 a.m. and drove towards the campsite. 3 hours later, her younger brother left their home and drove towards the same campsite at 82 km/h. When the younger brother reached the campsite at 7.45 p.m., Diana had another 4 km to travel. What was Diana’s average speed? Express your answer in mixed number.
Time that the Diana's younger brother started driving = 2.45 p.m.
Duration that Diana's younger brother drove from 2.45 p.m. to 7.45 p.m. = 5 h

Distance that Diana's younger brother travelled
= 5 x 82
= 410 km

Distance that Diana travelled by the time her younger brother reached the city
= 410 - 4
= 406 km

Time that Diana took to travel 406 km = 8 h

Diana's average speed
= 406 ÷ 8
= 50³₄ km/h

Answer(s): 50³₄ km/h