Mrs Chan left home at 8 a.m. and drove towards the city. 2⁵₁₂ hour later, Mr Chan left the house and drove at an average speed of 109 km/h towards the city. When Mr Chan reached his destination at 1 p.m., Mrs Chan was 12 km away from the city. Find Mrs Chan’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
⁵₁₂ h = ⁵₁₂ x 60 = 25 min
2⁵₁₂ = 2 h 25 min

2 h 25 min after 8 a.m. = 10.25 a.m.

Time that Mr Chan left the house = 10.25 a.m.

Time that Mr Chan took from 10.25 a.m. to 1 p.m. to reach his destination = 2 h 35 min

1 min = ¹₆₀ h
35 min = ³⁵₆₀ h = ⁷₁₂ h
2 h 35 min = 2⁷₁₂ h

Distance that Mr Chan drove
= 2⁷₁₂ x 109
= 281⁷₁₂ km

Distance that Mrs Chan drove when Mr Chan reached
= 281⁷₁₂ - 12 
= 269⁷₁₂ km

Time that Mrs Chan took to travel from 8 a.m. to 1 p.m. = 5 h

Mrs Chan's average speed
= 269⁷₁₂ ÷ 5
= 53¹¹₁₂ km/h

Answer(s): 53¹¹₁₂ km/h