Mrs Kong left home at 8 a.m. and drove towards the city. 1²₃ hour later, Mr Kong left the house and drove at an average speed of 82 km/h towards the city. When Mr Kong reached his destination at 3 p.m., Mrs Kong was 15 km away from the city. Find Mrs Kong’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
²₃ h = ²₃ x 60 = 40 min
1²₃ = 1 h 40 min

1 h 40 min after 8 a.m. = 9.40 a.m.

Time that Mr Kong left the house = 9.40 a.m.

Time that Mr Kong took from 9.40 a.m. to 3 p.m. to reach his destination = 5 h 20 min

1 min = ¹₆₀ h
20 min = ²⁰₆₀ h = ¹₃ h
5 h 20 min = 5¹₃ h

Distance that Mr Kong drove
= 5¹₃ x 82
= 437¹₃ km

Distance that Mrs Kong drove when Mr Kong reached
= 437¹₃ - 15 
= 422¹₃ km

Time that Mrs Kong took to travel from 8 a.m. to 3 p.m. = 7 h

Mrs Kong's average speed
= 422¹₃ ÷ 7
= 60¹₃ km/h

Answer(s): 60¹₃ km/h