Mrs Lim left home at 7 a.m. and drove towards the city. 1²₃ hour later, Mr Lim left the house and drove at an average speed of 82 km/h towards the city. When Mr Lim reached his destination at 2 p.m., Mrs Lim was 17 km away from the city. Find Mrs Lim’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 7 a.m. = 8.40 a.m.

Time that Mr Lim left the house = 8.40 a.m.

Time that Mr Lim took from 8.40 a.m. to 2 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 Lim drove
= 5¹₃ x 82
= 437¹₃ km

Distance that Mrs Lim drove when Mr Lim reached
= 437¹₃ - 17 
= 420¹₃ km

Time that Mrs Lim took to travel from 7 a.m. to 2 p.m. = 7 h

Mrs Lim's average speed
= 420¹₃ ÷ 7
= 60¹₂₁ km/h

Answer(s): 60¹₂₁ km/h