Mrs Yong left home at 8 a.m. and drove towards the city. 1¹₂ hour later, Mr Yong left the house and drove at an average speed of 99 km/h towards the city. When Mr Yong reached his destination at 1 p.m., Mrs Yong was 13 km away from the city. Find Mrs Yong’s average speed in km/h. Express your answer in mixed number.
1 h = 60 min 
¹₂ h = ¹₂ x 60 = 30 min
1¹₂ = 1 h 30 min

1 h 30 min after 8 a.m. = 9.30 a.m.

Time that Mr Yong left the house = 9.30 a.m.

Time that Mr Yong took from 9.30 a.m. to 1 p.m. to reach his destination = 3 h 30 min

1 min = ¹₆₀ h
30 min = ³⁰₆₀ h = ¹₂ h
3 h 30 min = 3¹₂ h

Distance that Mr Yong drove
= 3¹₂ x 99
= 346¹₂ km

Distance that Mrs Yong drove when Mr Yong reached
= 346¹₂ - 13 
= 333¹₂ km

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

Mrs Yong's average speed
= 333¹₂ ÷ 5
= 66⁷₁₀ km/h

Answer(s): 66⁷₁₀ km/h