Mrs Lim left home at 8 a.m. and drove towards the city. 1⁷₁₂ hour later, Mr Lim left the house and drove at an average speed of 89 km/h towards the city. When Mr Lim reached his destination at 3 p.m., Mrs Lim was 24 km away from the city. Find Mrs Lim’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
⁷₁₂ h = ⁷₁₂ x 60 = 35 min
1⁷₁₂ = 1 h 35 min

1 h 35 min after 8 a.m. = 9.35 a.m.

Time that Mr Lim left the house = 9.35 a.m.

Time that Mr Lim took from 9.35 a.m. to 3 p.m. to reach his destination = 5 h 25 min

1 min = ¹₆₀ h
25 min = ²⁵₆₀ h = ⁵₁₂ h
5 h 25 min = 5⁵₁₂ h

Distance that Mr Lim drove
= 5⁵₁₂ x 89
= 482¹₁₂ km

Distance that Mrs Lim drove when Mr Lim reached
= 482¹₁₂ - 24 
= 458¹₁₂ km

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

Mrs Lim's average speed
= 458¹₁₂ ÷ 7
= 65³⁷₈₄ km/h

Answer(s): 65³⁷₈₄ km/h